0001804220-21-000008 | 10-K | XBRL Viewer | Regeneron Pharmaceuticals INC


DOCUMENTS INCORPORATED BY REFERENCE

Specified portions of the Registrant's definitive proxy statement to be filed in connection with solicitation of proxies for its 2021 Annual Meeting of Shareholders are incorporated by reference into Part III of this Form 10-K. Exhibit index is located on pages 92 to 97 of this filing.

Entity Central Index Key

0000872589

Document Fiscal Year Focus

2020

Document Fiscal Period Focus

Amendment Flag

false

Class A Stock

Entity Information [Line Items]

Entity Common Stock, Shares Outstanding

1,848,970

Common Stock

Entity Information [Line Items]

Entity Common Stock, Shares Outstanding

105,282,929

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 2,193.7	$ 1,617.8
Marketable securities	1,393.3	1,596.5
Accounts receivable - trade, net	3,111.5	2,100.0
Inventories	1,916.6	1,415.5
Prepaid expenses and other current assets	160.8	273.7
Total current assets	9,779.1	7,689.1
Marketable securities	3,135.6	3,256.8
Property, plant, and equipment, net	3,221.6	2,890.4
Deferred tax assets	858.9	824.2
Other noncurrent assets	168.1	144.7
Total assets	17,163.3	14,805.2
Current liabilities:
Accounts payable	475.5	418.1
Accrued expenses and other current liabilities	1,521.8	1,211.4
Other liabilities - Sanofi	122.4	85.0
Total current liabilities	2,697.4	2,096.6
Long-term debt	1,978.5	0.0
Finance lease liabilities	717.2	713.9
Total liabilities	6,138.0	3,715.5
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred Stock, $.01 par value; 30,000,000 shares authorized; issued and outstanding - none	0.0	0.0
Additional paid-in capital	6,716.2	4,428.6
Retained earnings	10,893.0	7,379.8
Accumulated other comprehensive income	29.3	21.1
Treasury Stock, at cost; 16,431,520 shares in 2020 and 4,860,123 shares in 2019	(6,613.3)	(739.9)
Total stockholders' equity	11,025.3	11,089.7
Total liabilities and stockholders' equity	17,163.3	14,805.2
Class A Stock
Stockholders' equity:
Common stock	0.0	0.0
Common Stock
Stockholders' equity:
Common stock	0.1	0.1
Total stockholders' equity	0.1	0.1
Sanofi
Current assets:
Accounts receivable	404.7	260.6
Current liabilities:
Deferred revenue, current	341.7	310.5
Deferred revenue, noncurrent	16.7	27.7
Other noncurrent liabilities	189.3	482.0
Other
Current assets:
Accounts receivable	598.5	425.0
Current liabilities:
Deferred revenue, current	236.0	71.6
Deferred revenue, noncurrent	41.1	77.6
Other noncurrent liabilities	$ 497.8	$ 317.7

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
LIABILITIES AND STOCKHOLDERS' EQUITY
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized (in shares)	30,000,000	30,000,000
Preferred Stock, shares issued (in shares)	0	0
Preferred Stock, shares outstanding (in shares)	0	0
Treasury Stock (in shares)	16,431,520	4,860,123
Class A Stock
LIABILITIES AND STOCKHOLDERS' EQUITY
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	40,000,000	40,000,000
Common Stock, shares issued (in shares)	1,848,970	1,848,970
Common Stock, shares outstanding (in shares)	1,848,970	1,848,970
Common Stock
LIABILITIES AND STOCKHOLDERS' EQUITY
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	320,000,000	320,000,000
Common Stock, shares issued (in shares)	121,533,460	113,288,103

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Revenues	$ 8,497.1	$ 6,557.6	$ 5,145.6
Expenses:
Research and development	2,735.0	2,450.0	1,468.8
Selling, general, and administrative	1,346.0	1,341.9	1,127.2
Cost of goods sold and of collaboration and contract manufacturing		402.8	237.5
Other operating (income) expense, net	(280.4)	(209.2)	(402.3)
Total expenses	4,920.5	4,347.8	2,611.2
Income from operations	3,576.6	2,209.8	2,534.4
Other income (expense):
Other income (expense), net	290.7	249.5	47.3
Interest expense	(56.9)	(30.2)	(28.2)
Total other income (expense)	233.8	219.3	19.1
Income before income taxes	3,810.4	2,429.1	2,553.5
Income tax expense	297.2	313.3	109.1
Net income	$ 3,513.2	$ 2,115.8	$ 2,444.4
Net income per share - basic (in dollars per share)	$ 32.65	$ 19.38	$ 22.65
Net income per share - diluted (in dollars per share)	$ 30.52	$ 18.46	$ 21.29
Weighted average shares outstanding - basic (in shares)	107.6	109.2	107.9
Weighted average shares outstanding - diluted (in shares)	115.1	114.6	114.8
Statements of Comprehensive Income
Net income	$ 3,513.2	$ 2,115.8	$ 2,444.4
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on debt securities	9.1	35.9	(7.0)
Unrealized (loss) gain on cash flow hedges	(0.9)	(2.5)	0.7
Comprehensive income	3,521.4	2,149.2	2,438.1
Product
Revenues:
Revenues	5,567.6	4,834.4	4,106.2
Expenses:
Cost of goods sold and of collaboration and contract manufacturing	491.9	362.3	180.0
Collaboration and contract manufacturing
Expenses:
Cost of goods sold and of collaboration and contract manufacturing	628.0	402.8	237.5
Sanofi
Revenues:
Revenues		403.6	(125.7)
Sanofi \| Product and service, other
Revenues:
Revenues	1,186.4	403.6	(125.7)
Bayer
Revenues:
Revenues		1,145.6	1,036.1
Bayer \| Product and service, other
Revenues:
Revenues	1,186.1	1,145.6	1,036.1
Other
Revenues:
Revenues		174.0	129.0
Other \| Product and service, other
Revenues:
Revenues	$ 557.0	$ 174.0	$ 129.0

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock	Class A Stock	Common Stock
Beginning Balance (in shares) at Dec. 31, 2017								(3.8)	1.9	109.5
Beginning Balance at Dec. 31, 2017	$ 6,144.1	$ (143.4)	$ 3,512.9	$ 2,946.7	$ (136.8)	$ 0.6	$ (6.6)	$ (316.2)		$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock for equity awards granted under long-term incentive plans (in shares)										2.0
Issuance of Common Stock for equity awards granted under long-term incentive plans	114.2		114.2
Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations (in shares)										(0.5)
Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations	(187.2)		(187.2)
Issuance/distribution of Common Stock for 401(k) Savings Plan (in shares)										0.1
Issuance/distribution of Common Stock for 401(k) Savings Plan	26.9		26.9
Repurchases of Common Stock (in shares)								(0.2)
Repurchases of Common Stock	(80.2)							$ (80.2)
Stock-based compensation charges	444.8		444.8
Net income	2,444.4			2,444.4
Other comprehensive income (loss), net of tax	(6.3)					(6.3)
Ending Balance (in shares) at Dec. 31, 2018								(4.0)	1.9	111.1
Ending Balance at Dec. 31, 2018	8,757.3	$ 9.7	3,911.6	5,254.3	$ 9.7	(12.3)		$ (396.4)		$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock for equity awards granted under long-term incentive plans (in shares)										2.6
Issuance of Common Stock for equity awards granted under long-term incentive plans	213.2		213.2
Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations (in shares)										(0.5)
Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations	(188.0)		(188.0)
Issuance/distribution of Common Stock for 401(k) Savings Plan (in shares)								0.1
Issuance/distribution of Common Stock for 401(k) Savings Plan	38.1		24.9					$ 13.2
Repurchases of Common Stock (in shares)								(1.0)
Repurchases of Common Stock	(356.7)							$ (356.7)
Conversion of Class A Stock to Common Stock (in shares)									(0.1)	0.1
Conversion of Class A Stock to Common Stock	0.0
Stock-based compensation charges	466.9		466.9
Net income	2,115.8			2,115.8
Other comprehensive income (loss), net of tax	33.4					33.4
Ending Balance (in shares) at Dec. 31, 2019								(4.9)	1.8	113.3
Ending Balance at Dec. 31, 2019	11,089.7		4,428.6	7,379.8		21.1		$ (739.9)		$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Common Stock for equity awards granted under long-term incentive plans (in shares)										9.6
Issuance of Common Stock for equity awards granted under long-term incentive plans	2,576.4		2,576.4
Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations (in shares)										(1.4)
Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations	(768.9)		(768.9)
Issuance/distribution of Common Stock for 401(k) Savings Plan (in shares)								0.1
Issuance/distribution of Common Stock for 401(k) Savings Plan	44.7		37.2					$ 7.5
Repurchases of Common Stock (in shares)								(11.6)
Repurchases of Common Stock	(5,880.9)							$ (5,880.9)
Stock-based compensation charges	442.9		442.9
Net income	3,513.2			3,513.2
Other comprehensive income (loss), net of tax	8.2					8.2
Ending Balance (in shares) at Dec. 31, 2020								(16.4)	1.8	121.5
Ending Balance at Dec. 31, 2020	$ 11,025.3		$ 6,716.2	$ 10,893.0		$ 29.3		$ (6,613.3)		$ 0.1

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 3,513.2	$ 2,115.8	$ 2,444.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	235.9	210.3	148.2
Non-cash compensation expense	432.0	464.3	427.4
Other non-cash items, net	(135.0)	(29.3)	12.1
Deferred taxes	75.6	(130.6)	(140.0)
Changes in assets and liabilities:
Increase in trade, Sanofi, and other accounts receivable	(1,356.1)	(523.7)	(236.4)
Increase in inventories	(529.4)	(335.5)	(387.9)
Decrease (increase) in prepaid expenses and other assets	114.9	(79.8)	(88.1)
Increase (decrease) in deferred revenue	148.1	139.5	(43.4)
Increase in accounts payable, accrued expenses, and other liabilities	118.9	599.0	58.8
Total adjustments	(895.1)	314.2	(249.3)
Net cash provided by operating activities	2,618.1	2,430.0	2,195.1
Cash flows from investing activities:
Purchases of marketable and other securities	(3,241.0)	(3,202.4)	(1,845.5)
Sales or maturities of marketable and other securities	3,785.0	1,604.2	775.6
Capital expenditures	(614.6)	(429.6)	(383.1)
Other	0.0	0.0	(10.0)
Net cash used in investing activities	(70.6)	(2,027.8)	(1,463.0)
Cash flows from financing activities:
Proceeds from issuance of long-term debt, net of issuance costs	1,981.9	0.0	0.0
Proceeds from bridge loan facility	1,500.0	0.0	0.0
Repayment of bridge loan facility	(1,500.0)	0.0	0.0
Proceeds from issuance of Common Stock	2,575.2	211.8	114.5
Payments in connection with Common Stock tendered for employee tax obligations	(680.8)	(188.0)	(187.2)
Repurchases of Common Stock	(5,846.8)	(275.9)	(4.4)
Net cash used in financing activities	(1,970.5)	(252.1)	(77.1)
Net increase in cash, cash equivalents, and restricted cash	577.0	150.1	655.0
Cash, cash equivalents, and restricted cash at beginning of period	1,630.3	1,480.2	825.2
Cash, cash equivalents, and restricted cash at end of period	2,207.3	1,630.3	1,480.2
Supplemental disclosure of cash flow information
Cash paid for interest (net of amounts capitalized)	23.2	25.0	22.3
Cash paid for income taxes	$ 188.1	$ 342.3	$ 205.6

Business Overview and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Business Overview and Summary of Significant Accounting Policies

Organization and Business

Regeneron Pharmaceuticals, Inc. and its subsidiaries ("Regeneron," "Company," "we," "us," and "our") is a fully integrated biotechnology company that discovers, invents, develops, manufactures, and commercializes medicines for the treatment of serious diseases. Our commercialized medicines and product candidates in development are designed to help patients with eye diseases, allergic and inflammatory diseases, cancer, cardiovascular and metabolic diseases, pain, infectious diseases, and rare diseases. The Company's products that have received marketing approval consist of EYLEA® (aflibercept), Dupixent® (dupilumab), Libtayo® (cemiplimab), Praluent® (alirocumab), Kevzara® (sarilumab), Inmazeb™ (atoltivimab, maftivimab, and odesivimab-ebgn), ARCALYST® (rilonacept), and ZALTRAP® (ziv-aflibercept). In addition, REGEN-COV™ (casirivimab and imdevimab) received Emergency Use Authorization from the U.S. Food and Drug Administration ("FDA") for the treatment of mild to moderate COVID-19 in certain patients at high risk for progressing to severe COVID-19 and/or hospitalization. The Company is a party to collaboration agreements to develop and commercialize, as applicable, certain products and product candidates (see Note 3).

The Company operates in one business segment, which includes all activities related to the discovery, development, and commercialization of medicines for the treatment of serious diseases. The Company's business is subject to certain risks including, but not limited to, uncertainties relating to conducting research activities, product development, obtaining regulatory approvals, competition, and obtaining and enforcing patents.

Basis of Presentation

The consolidated financial statements include the accounts of Regeneron and its wholly-owned subsidiaries. Intercompany balances and transactions are eliminated in consolidation. Certain reclassifications have been made to prior period amounts to conform with the current period's presentation.

Effective January 1, 2020, we changed the presentation of cost reimbursements from collaborators who are not deemed to be our customers from collaboration revenue to a reduction of the corresponding operating expense (i.e., either Research and development or Selling, general, and administrative) incurred by us. We also changed the presentation of amounts recognized in connection with up-front and development milestone payments received from collaboration revenue to other operating income. We made these changes in presentation because we believe the new presentation is preferable, as it better reflects the nature of the Company’s costs incurred and revenues earned pursuant to arrangements with collaborators and enhances the comparability of our financial statements with industry peers.

The change in presentation has been applied retrospectively. The tables below present the impact of the change on the Company’s previously-filed Consolidated Balance Sheet as of December 31, 2019, the Consolidated Statement of Operations for the years ended December 31, 2019, and 2018, and the Consolidated Statement of Cash Flows for the years ended December 31, 2019, and 2018. The Company’s previously-filed balance sheet has been updated to reflect the addition of the caption Other liabilities for the presentation of up-front and development milestones paid by collaborators that are deferred. There was no impact on the Company’s previously-filed Consolidated Statements of Stockholders’ Equity.


	December 31, 2019
Balance Sheet Data:	As Previously Reported		Adjustments		As Revised
Accrued expenses and other current liabilities	$	1,086.8	$	124.6	$	1,211.4
Deferred revenue - Sanofi (current)	$	395.5	$	(85.0)	$	310.5
Deferred revenue - other (current)	$	196.2	$	(124.6)	$	71.6
Other liabilities - Sanofi (current)	—		$	85.0	$	85.0
Deferred revenue - Sanofi (noncurrent)	$	509.7	$	(482.0)	$	27.7
Deferred revenue - other (noncurrent)	$	109.3	$	(31.7)	$	77.6
Other liabilities - Sanofi (noncurrent)	—		$	482.0	$	482.0
Other noncurrent liabilities	$	286.0	$	31.7	$	317.7


	Year Ended December 31, 2019						Year Ended December 31, 2018
Statement of Operations Data:	As Previously Reported		Adjustments		As Revised		As Previously Reported		Adjustments		As Revised
Sanofi collaboration revenue	$	1,426.8	$	(1,023.2)	$	403.6	$	1,111.1	$	(1,236.8)	$	(125.7)
Bayer collaboration revenue	$	1,188.8	$	(43.2)	$	1,145.6	$	1,076.7	$	(40.6)	$	1,036.1
Other revenue	$	413.4	$	(239.4)	$	174.0	$	416.8	$	(287.8)	$	129.0
Total revenues	$	7,863.4	$	(1,305.8)	$	6,557.6	$	6,710.8	$	(1,565.2)	$	5,145.6

Research and development	$	3,036.6	$	(586.6)	$	2,450.0	$	2,186.1	$	(717.3)	$	1,468.8
Selling, general, and administrative	$	1,834.8	$	(492.9)	$	1,341.9	$	1,556.2	$	(429.0)	$	1,127.2
Cost of collaboration and contract manufacturing(1)	$	419.9	$	(17.1)	$	402.8	$	254.1	$	(16.6)	$	237.5
Other operating (income) expense, net	—		$	(209.2)	$	(209.2)	—		$	(402.3)	$	(402.3)
Total operating expenses	$	5,653.6	$	(1,305.8)	$	4,347.8	$	4,176.4	$	(1,565.2)	$	2,611.2

(1) In addition to the reclassification of certain amounts in connection with the change in accounting presentation described above, the Company also reclassified certain immaterial reimbursements that were previously classified as collaboration revenue to Cost of collaboration and contract manufacturing.


	Year Ended December 31, 2019						Year Ended December 31, 2018
Cash Flows Data:	As Previously Reported		Adjustments		As Revised		As Previously Reported		Adjustments		As Revised
Cash flows from operating activities:
Increase (decrease) in deferred revenue	$	294.0	$	(154.5)	$	139.5	$	(194.5)	$	151.1	$	(43.4)
Increase in accounts payable, accrued expenses, and other liabilities	$	444.5	$	154.5	$	599.0	$	209.9	$	(151.1)	$	58.8

We adopted Accounting Standards Codification ("ASC") 842, Leases, on January 1, 2019 (the "effective date") and used the effective date as our date of initial application. See Note 10. The new standard requires a lessee to recognize on its balance sheet (for both finance and operating leases) a liability for future lease payments and a right-of-use asset representing its right to use the underlying asset over the lease term. We elected the practical expedients upon transition, which permitted companies to not reassess lease identification, classification, and initial direct costs under the new standard for leases that commenced prior to the effective date. Upon adoption of the new standard, we recognized right-of-use assets of $33.2 million related to operating leases as of January 1, 2019. The impact of adopting the standard for the facilities that we had historically applied build-to-suit and capital lease accounting was not material to our Consolidated Financial Statements. Prior period amounts were not adjusted in connection with the adoption of this standard.

We adopted ASC 606, Revenue from Contracts with Customers, as of January 1, 2018. The Company adopted the standard using the modified retrospective method, and thus recognized a cumulative-effect adjustment to reduce Retained earnings and increase Deferred revenue on January 1, 2018 by $143.4 million, net of tax.

Use of Estimates

The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. The extent to which the COVID-19 pandemic may directly or indirectly impact our business, financial condition, and results of operations is highly uncertain and subject to change. We considered the potential impact of the COVID-19 pandemic on our estimates and assumptions and there was not a material impact to our consolidated

financial statements as of and for the year ended December 31, 2020; however, actual results could differ from those estimates and there may be changes to our estimates in future periods.

Concentration of Credit Risk

Financial instruments which potentially expose the Company to concentrations of credit risk consist of cash, cash equivalents, certain investments, and accounts receivable. In accordance with the Company's policies, the Company mandates asset diversification and monitors exposure with its counterparties.

Concentrations of credit risk with respect to accounts receivable are significant. The Company has a concentration of credit risk associated with the receivables due from its collaborators Bayer, Sanofi, and Teva. The Company is also subject to credit risk with accounts receivable from its product sales to its customers. As of December 31, 2020 and 2019, three individual customers accounted for 93% and 97%, respectively, of the Company's net trade accounts receivable balances. The Company has contractual payment terms with each of its collaborators and customers, and the Company monitors their financial performance and credit worthiness so that it can properly assess and respond to any changes in their credit profile. As of December 31, 2020 and 2019, there were no write-offs and allowances of accounts receivable related to credit risk for our collaborators or customers.

Significant Accounting Policies

Cash and Cash Equivalents

The Company considers all highly liquid debt instruments with a maturity of three months or less when purchased to be cash equivalents. The carrying amount reported in the Consolidated Balance Sheet for cash and cash equivalents approximates its fair value.

Debt and Equity Securities

The Company has an investment policy that includes guidelines on acceptable investment securities, minimum credit quality, maturity parameters, and concentration and diversification. We invest our cash primarily in debt securities of investment grade institutions. We consider our investments in debt securities to be "available-for-sale," as defined by authoritative guidance issued by the Financial Accounting Standards Board ("FASB"). These assets are carried at fair value and the unrealized gains and losses are included in Accumulated other comprehensive income (loss). Realized gains and losses on available-for-sale debt securities are included in Other income (expense), net. The Company reviews its portfolio of available-for-sale debt securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost have resulted from a credit-related loss or other factors. If the decline in fair value is due to credit-related factors, a loss is recognized in net income, whereas if the decline in fair value is not due to credit-related factors, the loss is recorded in Other comprehensive income (loss).

We also have investments in equity securities that are carried at fair value with changes in fair value recognized within Other income (expense), net. We have elected to measure certain equity investments we hold that do not have readily determinable fair values at cost less impairment, if any, and adjust for observable price changes in orderly transactions for identical or similar investments of the same issuer within Other income (expense), net.

Accounts Receivable

The Company's trade accounts receivable arise from product sales and represent amounts due from its customers, which are all located in the United States. In addition, the Company records accounts receivable arising from its collaboration and licensing agreements. The Company monitors the financial performance and credit worthiness of its counterparties so that it can properly assess and respond to changes in their credit profile. The Company provides allowances against receivables for estimated losses, if any, that may result from a counterparty's inability to pay. Amounts determined to be uncollectible are written-off against the allowance.

Inventories

Inventories are stated at the lower of cost or net realizable value. The Company determines the cost of inventory using the first-in, first-out, or FIFO, method.

The Company capitalizes inventory costs associated with the Company's products prior to regulatory approval when, based on management's judgment, future commercialization is considered probable and the future economic benefit is expected to be realized; otherwise, such costs are expensed. The determination to capitalize inventory costs is based on various factors, including status and expectations of the regulatory approval process, any known safety or efficacy concerns, potential labeling restrictions, and any other impediments to obtaining regulatory approval.

The Company periodically analyzes its inventory levels to identify inventory that may expire prior to expected sale or has a cost basis in excess of its estimated realizable value, and writes-down such inventories as appropriate. In addition, the Company's products are subject to strict quality control and monitoring which the Company performs throughout the manufacturing process. If certain batches or units of product no longer meet quality specifications or become obsolete due to expiration, the Company records a charge to write down such unmarketable inventory to its estimated realizable value.

Property, Plant, and Equipment

Property, plant, and equipment are stated at cost, net of accumulated depreciation. Depreciation is calculated on a straight-line basis over the estimated useful lives of the assets. Leasehold improvements are amortized over the shorter of the estimated useful lives of the assets or the remaining lease term. Costs of construction of certain long-lived assets include capitalized interest, which is amortized over the estimated useful life of the related asset. Expenditures for maintenance and repairs which do not materially extend the useful lives of the assets are charged to expense as incurred. The cost and accumulated depreciation or amortization of assets retired or sold are removed from the respective accounts, and any gain or loss is recognized in operations. The estimated useful lives of property, plant, and equipment are as follows:


Building and improvements						10–50 years
Laboratory and other equipment						3–10 years
Furniture and fixtures						5 years

The Company periodically assesses the recoverability of long-lived assets, such as property, plant, and equipment, and evaluates such assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable.

Leases

The Company determines if an arrangement is a lease considering whether there is an identified asset and the contract conveys the right to control its use. Leases with an initial term of 12 months or less are not recorded on the balance sheet. The Company's lease terms may include options to extend or terminate a lease when it is reasonably certain that it will exercise that option. The Company accounts for lease components (e.g., rental payments) separately from non-lease components (e.g., common area maintenance costs).

Right-of-use assets and lease liabilities are recognized at lease commencement date based on the present value of lease payments over the lease term, unless there is a transfer of title or purchase option we are reasonably certain to exercise. For leases where an implicit rate is not readily determinable, we use our incremental borrowing rate based on information available at the lease commencement date to determine the present value of future lease payments. Lease expense for operating leases is recognized on a straight-line basis over the expected lease term.

Revenue Recognition - Product Revenue

Revenue from product sales is recognized at a point in time when our customer is deemed to have obtained control of the product, which generally occurs upon receipt by our customer.

The amount of revenue we recognize from product sales may vary due to rebates, chargebacks, and discounts provided under governmental and other programs, distribution-related fees, and other sales-related deductions. In order to determine the transaction price, we estimate, utilizing the expected value method, the amount of variable consideration that we will be entitled to. This estimate is based upon contracts with customers, healthcare providers, payors, and government agencies, statutorily-defined discounts applicable to government-funded programs, historical experience, estimated payor mix, and other relevant factors. The Company reviews its estimates of rebates, chargebacks, and other applicable provisions each period and records any necessary adjustments in the current period's net product sales.

•Rebates, Chargebacks, and Discounts: The Company estimates reductions to product sales for Medicaid and Veterans' Administration ("VA") programs as well as certain other qualifying federal and state government programs, and other programs, including group purchasing organizations, and records an allowance for rebates and chargebacks. The Company's liability for Medicaid rebates consists of estimates for claims that a state will make for a current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, and invoices received for claims from prior quarters that have not been paid. The Company's reserves related to discounted pricing to VA, Public Health Services, eligible physicians, and others (collectively "qualified healthcare providers") represent the Company's estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices the Company charges to its customers (i.e., distributors and specialty pharmacies). The Company's customers charge the Company for the difference between what they pay for the products and the ultimate selling price to the qualified healthcare providers. The Company's reserve for this discounted pricing is based on expected sales to qualified healthcare providers and the chargebacks that customers have already claimed.

•Distribution-Related Fees: The Company has written contracts with its customers that include terms for distribution-related fees. The Company estimates and records distribution and related fees due to its customers generally based on gross sales.

•Other Sales-Related Deductions: The Company's other sales-related deductions include co-pay assistance programs and product returns. The Company estimates and records other sales-related deductions generally based on gross sales, written contracts, and other relevant factors.

Consistent with industry practice, the Company offers its customers a limited right to return product purchased directly from the Company, which is principally based upon the product's expiration date. Product returned is generally not resalable given the nature of the Company's products and method of administration. The Company develops estimates for product returns based upon historical experience, shelf life of the product, and other relevant factors. The Company monitors product supply levels in the distribution channel, as well as sales by its customers, using product-specific data provided by its customers. If necessary, the Company's estimates of product returns may be adjusted in the future based on actual returns experience, known or expected changes in the marketplace, or other factors.

Collaborative Arrangements

We have entered into various collaborative arrangements to research, develop, manufacture, and commercialize product candidates and utilize our technology platforms. Although each of these arrangements is unique in nature, such arrangements involve a joint operating activity where both parties are active participants in the activities of the collaboration and exposed to significant risks and rewards dependent on the commercial success of the activities.

In arrangements where we do not deem our collaborator to be our customer, payments to and from our collaborator are presented in our statement of operations based on the nature of our business operations, the nature of the arrangement, including the contractual terms, and the nature of the payments, as summarized in the table and further described below.


Nature/Type of Payment						Statement of Operations Presentation
Regeneron's share of profits or losses in connection with commercialization of products						Collaboration revenue
Reimbursement for manufacturing of commercial supplies						Collaboration revenue
Royalties and/or sales-based milestones earned						Collaboration revenue
Reimbursement of Regeneron's research and development expenses						Reduction to Research and development expenses
Regeneron's obligation for its share of collaborator's research and development expenses						Research and development expense
Up-front and development milestone payments to collaborators						Research and development expense
Reimbursement of Regeneron's commercialization-related expenses						Reduction to Selling, general, and administrative expense
Regeneron's obligation for its share of collaborator's commercialization-related expenses						Selling, general, and administrative expense
Regeneron's obligation to pay collaborator for its share of gross profits when Regeneron is deemed to be the principal						Cost of goods sold
Up-front and development milestones earned (when we have a combined unit of account which includes a license and providing research and development services)						Other operating income

In agreements involving multiple goods or services promised to be transferred to our collaborator, we must assess, at the inception of the contract, whether each promise represents a separate obligation (i.e., is "distinct"), or whether such promises should be combined as a single unit of account. When we have a combined unit of account which includes a license and providing research and development services to our collaborator, recognition of up-front payments and development milestones earned from our collaborator is deferred (as a liability) and recognized over the development period (i.e., over time). In arrangements where we satisfy our obligation(s) during the development phase over time, we recognize amounts initially deferred over time typically using an input method on the basis of our research and development costs incurred relative to the total expected cost which determines the extent of our progress toward completion. We review our estimates each period and make revisions to such estimates as necessary. We recognized other operating income in connection with up-front and development milestones earned, for which we used an input method, of $276.7 million and $207.2 million for the years ended December 31, 2020 and 2019, respectively.

When we are entitled to reimbursement of all or a portion of the expenses (e.g., research and development expenses) that we incur under a collaboration, we record those reimbursable amounts in the period in which such costs are incurred.

If we and our collaborator perform development work or commercialization-related activities and share costs, we also recognize, as expense (i.e., research and development expense or selling, general, and administrative expense, as applicable) in the period when our collaborator incurs such expenses, the portion of the collaborator's expenses that we are obligated to reimburse. Our collaborators provide us with estimated expenses for the most recent fiscal quarter. Our collaborators' estimates are reconciled to their actual expenses for such quarter in the subsequent fiscal quarter, and our portion of our collaborators' expenses that we are obligated to reimburse is adjusted on a prospective basis accordingly, as necessary.

Under certain of the Company's collaboration agreements, product sales and cost of sales may be recorded by the Company's collaborators as they are deemed to be the principal in the transaction. In arrangements where we:

•are obligated to use commercially reasonable efforts to supply commercial product to our collaborator, we may be reimbursed for our manufacturing costs as commercial product is shipped to the collaborator; however, recognition of such cost reimbursements is recognized when the product is sold by our collaborator to third-party customers;

•share in any profits or losses arising from the commercialization of such products, we record our share of the variable consideration, representing net product sales less cost of goods sold and shared commercialization and other expenses, in the period in which such underlying sales occur and costs are incurred by the collaborator; and

•receive royalties and/or sales-based milestone payments from our collaborator, we recognize such amounts in the period earned.

Our collaborators provide us with estimates of product sales and our share of profits or losses, as applicable, for such quarter. These estimates are reconciled to actual results in the subsequent fiscal quarter, and collaboration revenue is adjusted accordingly, as necessary.

Research and Development Expenses

Research and development expenses include costs attributable to the conduct of research and development programs, including the cost of salaries, payroll taxes, employee benefits, materials, supplies, depreciation on and maintenance of research equipment, costs related to research collaboration and licensing agreements, the cost of services provided by outside contractors, including services related to the Company's clinical trials, clinical trial expenses, the full cost of manufacturing drug for use in research, preclinical development, and clinical trials, amounts that the Company is obligated to reimburse to collaborators for research and development expenses that they incur, and the allocable portions of facility costs, such as rent, utilities, insurance, repairs and maintenance, depreciation, and general support services. Costs associated with research and development are expensed.

For each clinical trial that we conduct, certain clinical trial costs are expensed immediately, while others are expensed over time based on the expected total number of patients in the trial, the rate at which patients enter the trial, and/or the period over which clinical investigators, contract research organizations ("CROs"), or other third-party service providers are expected to provide services. In the event of early termination of a clinical trial, we accrue and recognize expenses in an amount based on our estimate of the remaining noncancelable obligations associated with the winding down of the clinical trial and/or penalties.

Stock-based Compensation

The Company recognizes stock-based compensation expense for equity grants under the Company's long-term incentive plans to employees and non-employee members of the Company's board of directors (as applicable) based on the grant-date fair value of those awards. The grant-date fair value of an award is generally recognized as compensation expense over the award's requisite service period.

The fair value of stock option awards is estimated using the Black-Scholes model. Stock-based compensation expense also includes an estimate, which is made at the time of grant, of the number of awards that are expected to be forfeited. This estimate is revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.

The fair value of performance-based restricted stock units which are subject to vesting based on the Company’s attainment of pre-established market performance goals is estimated using a Monte Carlo simulation. The probability of the number of actual shares expected to be earned is considered in the grant-date valuation, and therefore, stock-based compensation expense is not adjusted at the vesting date to reflect the actual number of shares earned.

Income Taxes

The provision for income taxes includes U.S. federal, state, local, and foreign taxes. Income taxes are accounted for under the liability method. Deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns, including deferred tax assets and liabilities for expected amounts of global intangible low-taxed income ("GILTI") inclusions, are recognized on the difference between the tax basis of assets and liabilities and their respective financial reporting amounts ("temporary differences") at enacted tax rates in effect for the years in which the differences are expected to reverse. A valuation allowance is established for deferred tax assets for which it is more likely than not that some portion or all of the deferred tax assets will not be realized.

Uncertain tax positions, for which management's assessment is that there is more than a 50% probability that the position will be sustained upon examination by a taxing authority based upon its technical merits, are subjected to certain recognition and measurement criteria. The Company re-evaluates uncertain tax positions and considers various factors, including, but not limited to, changes in tax law, the measurement of tax positions taken or expected to be taken in tax returns, and changes in facts or circumstances related to a tax position. The Company adjusts the level of the liability to reflect any subsequent changes in the relevant facts and circumstances surrounding the uncertain positions. The Company recognizes interest and penalties related to income tax matters in income tax expense.

Per Share Data

Basic net income per share is computed by dividing net income by the weighted average number of shares of Common Stock and Class A Stock outstanding. Net income per share is presented on a combined basis, inclusive of Common Stock and Class A Stock outstanding, as each class of stock has equivalent economic rights. Basic net income per share excludes restricted stock until vested. Diluted net income per share includes the potential dilutive effect of common stock equivalents as if such securities were converted or exercised during the period, when the effect is dilutive. Common stock equivalents include: (i) outstanding stock options and unvested restricted stock under the Company's long-term incentive plans, which are included under the treasury stock method when dilutive, and (ii) Common Stock that would be issued upon the achievement of certain market conditions, which are included under the treasury stock method when dilutive.

Recently Adopted Accounting Standards

We adopted Accounting Standards Update 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), as of January 1, 2020. ASU 2016-13 requires an entity to measure and recognize expected credit losses for certain financial instruments, including trade receivables, as an allowance that reflects the entity's current estimate of credit losses expected to be incurred. For available-for-sale debt securities with unrealized credit losses, the standard requires allowances to be recorded through net income instead of directly reducing the amortized cost of the investment under the previous other-than-temporary impairment model. The adoption of this standard did not have a material impact on our financial statements or a significant impact on our internal controls.

Product Sales

12 Months Ended

Dec. 31, 2020

Revenues [Abstract]

Product Sales

Net product sales consist of the following:


	Year Ended December 31,
Net Product Sales in the United States	2020		2019		2018
EYLEA	$	4,947.2	$	4,644.2	$	4,076.7
Libtayo	270.7		175.7		14.8
Praluent	150.9		*		*
REGEN-COV	185.7		—		—
ARCALYST	13.1		14.5		14.7
	$	5,567.6	$	4,834.4	$	4,106.2

* Effective April 1, 2020, the Company is solely responsible for the development and commercialization of Praluent in the United States and records net product sales of Praluent in the United States. See Note 3 for further details.

The Company had product sales to certain customers that accounted for more than 10% of total gross product revenue for each of the years ended December 31, 2020, 2019, and 2018. Sales to each of these customers as a percentage of the Company's total gross product revenue are as follows:


	Year Ended December 31,
	2020		2019		2018
Besse Medical, a subsidiary of AmerisourceBergen Corporation	51	%	57	%	56	%
McKesson Corporation	32	%	33	%	36	%

Revenue from product sales is recorded net of applicable provisions for rebates, chargebacks, and discounts, distribution-related fees, and other sales-related deductions. Accruals for chargebacks and discounts are recorded as a direct reduction to accounts receivable. Accruals for rebates, distribution-related fees, and other sales-related deductions are recorded within accrued liabilities.

The following table summarizes the provisions, and credits/payments, for sales-related deductions for the years ended December 31, 2020, 2019, and 2018.


	Rebates, Chargebacks, and Discounts		Distribution- Related Fees		Other Sales- Related Deductions		Total
Balance as of December 31, 2017	$	29.9	$	34.1	$	21.3	$	85.3
Provisions	223.4		211.0		44.5		478.9
Credits/payments	(212.2)		(203.1)		(57.5)		(472.8)
Balance as of December 31, 2018	41.1		42.0		8.3		91.4
Provisions	423.2		242.9		61.8		727.9
Credits/payments	(384.0)		(238.5)		(40.7)		(663.2)
Balance as of December 31, 2019	80.3		46.4		29.4		156.1
Provisions	762.9		279.9		94.1		1,136.9
Credits/payments	(641.0)		(249.1)		(78.7)		(968.8)
Balance as of December 31, 2020	$	202.2	$	77.2	$	44.8	$	324.2

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Section 50
-Paragraph 10
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 13
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-Topic 606
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-Section 50
-Paragraph 12
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Paragraph 15
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Section 50
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

+ Details

Collaboration, License, and Other Agreements

12 Months Ended

Dec. 31, 2020

Revenue from Contract with Customer [Abstract]

Collaboration and License Agreements

Collaboration, License, and Other Agreements

a. Sanofi

Amounts recognized in our Statements of Operations in connection with our collaborations with Sanofi are detailed below:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Antibody:
Regeneron's share of profits (losses) in connection with commercialization of antibodies	Sanofi collaboration revenue	$	785.2	$	209.3	$	(227.0)
Sales-based milestone earned	Sanofi collaboration revenue	$	50.0	—		—
Reimbursement for manufacturing of commercial supplies	Sanofi collaboration revenue	$	368.0	$	216.0	$	113.7
Reimbursement of research and development expenses	Reduction of Research and development expense	$	226.7	$	277.7	$	265.3
Regeneron's obligation for its share of Sanofi research and development expenses	Research and development expense	$	(77.6)	$	(46.0)	$	(47.7)
Reimbursement of commercialization-related expenses	Reduction of Selling, general, and administrative expense	$	359.4	$	479.9	$	417.2
Regeneron's obligation for its share of Sanofi other expenses	Cost of collaboration and contract manufacturing	$	(21.5)	$	(12.8)	$	(16.1)

Immuno-oncology:
Regeneron's share of losses in connection with commercialization of Libtayo outside the United States	Sanofi collaboration revenue	$	(25.7)	$	(21.7)	$	(12.4)
Reimbursement for manufacturing of commercial supplies	Sanofi collaboration revenue	$	8.9	—		—
Reimbursement of research and development expenses	Reduction of Research and development expense	$	166.2	$	163.0	$	311.8
Reimbursement of commercialization-related expenses	Reduction of Selling, general, and administrative expense	$	64.7	$	10.3	$	8.9
Regeneron's obligation for Sanofi's share of Libtayo U.S. gross profits	Cost of goods sold	$	(119.1)	$	(78.2)	$	(6.8)
Amounts recognized in connection with up-front payments received	Other operating income	$	210.6	$	92.7	$	243.8

See Note 9 and Note 11 for information regarding Sanofi's sale of our Common Stock during the second quarter of 2020.

Antibody

The Company is party to a global, strategic collaboration with Sanofi to research, develop, and commercialize fully human monoclonal antibodies (the "Antibody Collaboration"), which currently consists of Dupixent, Kevzara, and itepekimab. Under the terms of the Antibody License and Collaboration Agreement ("LCA"), Sanofi is generally responsible for funding 80%–100% of agreed-upon development costs. We are obligated to reimburse Sanofi for 30%–50% of worldwide development expenses that were funded by Sanofi (collectively, the "development balance") based on our share of collaboration profits from commercialization of collaboration products. However, we are only required to apply 10% of our share of the profits from the Antibody Collaboration in any calendar quarter to reimburse Sanofi for these development costs. The Company's contingent reimbursement obligation to Sanofi under the Antibody Collaboration was approximately $3.103 billion as of December 31, 2020.

Effective January 2018, the Company and Sanofi entered into a letter agreement (the "Letter Agreement") in connection with, among other matters, the allocation of additional funds to certain activities relating to dupilumab and itepekimab (collectively,

the "Dupilumab/Itepekimab Eligible Investments"). Refer to the "Immuno-Oncology" section below for further details regarding the Letter Agreement and Note 11 for additional information regarding shares purchased by us from Sanofi.

Regeneron is obligated to use commercially reasonable efforts to supply clinical requirements of each drug candidate under the Antibody Collaboration until commercial supplies of that drug candidate are being manufactured. Sanofi leads commercialization activities for products under the Antibody Collaboration, subject to the Company's right to co-commercialize such products. The Company co-commercializes Dupixent in the United States and exercised its option to co-commercialize Dupixent in certain countries outside the United States. We currently anticipate commencing co-commercialization of Dupixent in such countries outside the United States in 2021. The parties equally share profits and losses from sales within the United States. The parties share profits outside the United States on a sliding scale based on sales starting at 65% (Sanofi)/35% (Regeneron) and ending at 55% (Sanofi)/45% (Regeneron), and losses outside the United States at 55% (Sanofi)/45% (Regeneron).

In addition to profit and loss sharing, we are entitled to receive sales milestone payments from Sanofi. In the third quarter of 2020, the Company earned, and recognized as revenue, the first $50.0 million sales-based milestone from Sanofi, upon aggregate annual sales of Dupixent, Kevzara, and Praluent outside the United States exceeding $1.0 billion on a rolling twelve-month basis. We are entitled to receive up to an aggregate of $200.0 million in additional milestone payments from Sanofi, including the second sales milestone in the amount of $50.0 million, when such sales outside the United States exceed $1.5 billion on a rolling twelve-month basis.

In April 2020, the Company and Sanofi entered into an amendment to the LCA in connection with, among other things, the removal of Praluent from the LCA such that (i) effective April 1, 2020, the LCA no longer governs the development, manufacture, or commercialization of Praluent and (ii) the quarterly period ended March 31, 2020 was the last quarter for which Sanofi and the Company shared profits and losses for Praluent under the LCA. The parties also entered into a Praluent Cross License & Commercialization Agreement (the "Praluent Agreement") pursuant to which, effective April 1, 2020, the Company, at its sole cost, is solely responsible for the development and commercialization of Praluent in the United States, and Sanofi, at its sole cost, is solely responsible for the development and commercialization of Praluent outside of the United States. Under the Praluent Agreement, Sanofi will pay the Company a 5% royalty on Sanofi’s net product sales of Praluent outside the United States until March 31, 2032. The Company will not owe Sanofi royalties on the Company’s net product sales of Praluent in the United States. Although each party will be responsible for manufacturing Praluent for its respective territory, the parties have entered into definitive supply agreements under which, for a certain transitional period, the Company will continue to supply drug substance to Sanofi and Sanofi will continue to supply finished product to Regeneron. With respect to any intellectual property or product liability litigation relating to Praluent, the parties have agreed that, effective April 1, 2020, Regeneron and Sanofi each will be solely responsible for any such litigation (including damages and other costs and expenses thereof) in the United States and outside the United States, respectively, arising out of Praluent sales or other activities on or after April 1, 2020 (subject to Sanofi's right to set off a portion of any third-party royalty payments resulting from certain patent litigation proceedings against up to 50% of any Praluent royalty payment owed to Regeneron). The parties will each bear 50% of any damages arising out of Praluent sales or other activities prior to April 1, 2020. See Note 15 for discussion of legal proceedings related to Praluent.

The Company's significant promised goods and services in connection with the Antibody Collaboration consist of providing research and development services, including the manufacturing of clinical supplies, and providing commercial-related services, including the manufacturing of commercial supplies. We recognize amounts in connection with the Antibody Collaboration based on the amount we have the right to invoice and such amount corresponds directly with our performance to date; therefore, we do not disclose the value of the transaction price (i.e., the amount of consideration we expect to be entitled to) allocated to our remaining unsatisfied obligations.

The following table summarizes contract balances in connection with the Company's Antibody Collaboration with Sanofi:


	As of December 31,
	2020		2019
Accounts receivable	$	407.7	$	272.7
Deferred revenue	$	347.7	$	328.8

Immuno-Oncology

The Company is party to a collaboration with Sanofi to research, develop, and commercialize antibody-based cancer treatments in the field of immuno-oncology (the "IO Collaboration"). The IO Collaboration is governed by an Amended and Restated Immuno-oncology Discovery and Development Agreement ("Amended IO Discovery Agreement"), and an Immuno-oncology License and Collaboration Agreement ("IO License and Collaboration Agreement"). In connection with the execution of the original Immuno-oncology Discovery and Development Agreement in 2015 ("2015 IO Discovery Agreement"), which has been replaced by the Amended IO Discovery Agreement (as discussed below), Sanofi made a $265.0 million non-refundable up-front payment to the Company. Pursuant to the 2015 IO Discovery Agreement, the Company was to spend up to $1.090 billion to identify and validate potential immuno-oncology targets and develop therapeutic antibodies against such targets through clinical proof-of-concept, and Sanofi was to reimburse the Company for up to $825.0 million of these costs, subject to certain annual limits.

We are obligated to reimburse Sanofi for half of the development costs they funded that are attributable to clinical development of antibody product candidates from our share of future profits from commercialized IO Collaboration products. However, the Company is only required to apply 10% of its share of the profits from IO Collaboration products in any calendar quarter towards reimbursing Sanofi for these development costs. The Company's contingent reimbursement obligation to Sanofi under the IO Collaboration was approximately $107 million as of December 31, 2020.

Effective December 31, 2018, the Company and Sanofi entered into the Amended IO Discovery Agreement, which narrowed the scope of the existing discovery and development activities conducted by the Company ("IO Development Activities") under the 2015 IO Discovery Agreement to developing therapeutic bispecific antibodies targeting (i) BCMA and CD3 (the "BCMAxCD3 Program") and (ii) MUC16 and CD3 (the "MUC16xCD3 Program") through clinical proof-of-concept. The Amended IO Discovery Agreement provided for Sanofi’s payment of $461.9 million to the Company as consideration for (x) the termination of the 2015 IO Discovery Agreement, (y) the prepayment for certain IO Development Activities regarding the BCMAxCD3 Program and the MUC16xCD3 Program, and (z) the reimbursement of costs incurred by the Company under the 2015 IO Discovery Agreement during the fourth quarter of 2018.

Under the terms of the Amended IO Discovery Agreement, the Company is required to conduct development activities with respect to (i) the BCMAxCD3 Program through the earlier of clinical proof-of-concept or the expenditure of $70.0 million (the "BCMAxCD3 Program Costs Cap") and (ii) the MUC16xCD3 Program through the earlier of clinical proof-of-concept or the expenditure of $50.0 million (the "MUC16xCD3 Program Costs Cap").

With regard to the BCMAxCD3 Program and the MUC16xCD3 Program, when (i) clinical proof-of-concept is established, (ii) the applicable Program Costs Cap is reached, or (iii) in certain other limited circumstances, Sanofi will have the option to license rights to the product candidate and other antibodies targeting the same targets for, with regard to BCMAxCD3, immuno-oncology indications, and with regard to MUC16xCD3, all indications, pursuant to the IO License and Collaboration Agreement, as amended. Given the applicable Program Costs Cap for the BCMAxCD3 Program and MUC16xCD3 Program has been reached, we expect Sanofi to provide its decision on whether it will exercise its option to license rights to these product candidates in early 2021. If Sanofi does not exercise its option to license rights to a product candidate, we will retain the exclusive right to develop and commercialize such product candidate and Sanofi will receive a royalty on sales. Pursuant to the Amended IO Discovery Agreement, the parties agreed that (i) if Sanofi exercises its option with respect to a BCMAxCD3 Program antibody, Sanofi will lead the development and global commercialization of such BCMAxCD3 Program antibody; and (ii) if Sanofi exercises its option with respect to a MUC16xCD3 Program antibody, (x) we will lead the development of such MUC16xCD3 Program antibody and commercialization of such MUC16xCD3 Program antibody within the United States and (y) Sanofi will lead the commercialization of such MUC16xCD3 Program antibody outside of the United States.

If Sanofi exercises its option to license rights to a BCMAxCD3 Program antibody or MUC16xCD3 Program antibody thereunder, it will co-develop these drug candidates with the Company through product approval. Sanofi will fund development costs up front for a BCMAxCD3 Program antibody and we will reimburse half of the total development costs for such antibody from our share of future IO Collaboration profits to the extent they are sufficient for this purpose, subject to the same 10% reimbursement provision described above. In addition, we and Sanofi will share equally, on an ongoing basis, the development costs for a MUC16xCD3 Program antibody.

In connection with the execution of the IO License and Collaboration Agreement in 2015, Sanofi made a $375.0 million non-refundable up-front payment to the Company. Under the terms of the IO License and Collaboration Agreement, the parties are co-developing and co-commercializing Libtayo (cemiplimab), an antibody targeting the receptor known as programmed cell death protein 1 (PD-1). The parties share equally, on an ongoing basis, agreed-upon development and commercialization

expenses for Libtayo. Pursuant to the Letter Agreement, the Libtayo development budget was increased and the Company allowed Sanofi to satisfy in whole or in part its funding obligations with respect to the Libtayo development and Dupilumab/Itepekimab Eligible Investments incurred in periods through September 30, 2020 by selling certain shares of our Common Stock directly or indirectly owned by Sanofi; if Sanofi desired to sell such shares, we were able to elect to purchase, in whole or in part, such shares from Sanofi. See Note 11 for additional information regarding shares purchased by us from Sanofi.

The Company has principal control over the development of Libtayo and leads commercialization activities in the United States (see Note 2 for related product sales information), while Sanofi leads commercialization activities outside of the United States. Sanofi has exercised its option to co-commercialize Libtayo in the United States.

The Company will be entitled to a milestone payment of $375.0 million in the event that global sales of certain licensed products targeting PD-1 (including Libtayo), together with sales of any other products licensed under the IO License and Collaboration Agreement and sold for use in combination with any of such licensed products targeting PD-1, equal or exceed $2.0 billion in any consecutive twelve-month period.

In August 2018, we and Sanofi entered into a license agreement with Bristol-Myers Squibb Company, E. R. Squibb & Sons, L.L.C., and Ono Pharmaceutical Co., Ltd. to obtain a license under certain patents owned and/or exclusively licensed by one or more of those parties that includes the right to develop and sell Libtayo. Under the agreement, we and Sanofi made an up-front payment of $20.0 million and are obligated to pay royalties of 8.0% on worldwide sales of Libtayo through December 31, 2023, and royalties of 2.5% from January 1, 2024 through December 31, 2026. The up-front payment was shared, and the royalties are shared, equally by us and Sanofi.

Each party will have the right to co-commercialize licensed products in countries where it is not the lead commercialization party. The parties share equally in profits and losses in connection with the commercialization of collaboration products. The Company is obligated to use commercially reasonable efforts to supply clinical requirements of each drug candidate under the IO License and Collaboration Agreement until commercial supplies of that IO drug candidate are being manufactured.

At the inception of the IO Collaboration, the Company's significant promised goods and services consisted of a license to certain rights and intellectual property and providing research and development services, including the manufacturing of clinical supplies. The Company concluded that the license was not distinct, primarily as a result of (i) Sanofi being unable to benefit on its own or together with other resources that are readily available as the license provides access to Regeneron's complex and specialized know-how and (ii) the research and development services, including manufacturing in support of such services, were expected to significantly modify the initial license. Therefore, the promised goods and services were considered a combined unit of account. Consequently, the $640.0 million in aggregate up-front payments made by Sanofi during 2015 in connection with the execution of the IO Collaboration was recorded within other liabilities and has been included in the transaction price.

During 2020, we updated our estimate of the total research and development costs expected to be incurred (which resulted in a change to the estimate of the stage of completion) in connection with the Sanofi IO Collaboration, and, as a result, recorded a cumulative catch-up adjustment of $135.4 million to other operating income. During 2018, we updated our estimate of the total research and development costs expected to be incurred for this arrangement, including in connection with the termination of the 2015 IO Discovery Agreement, and, as result, a cumulative catch-up adjustment of $135.0 million was recorded to other operating income.

The following table summarizes contract balances in connection with the Company's IO Collaboration with Sanofi:


	As of December 31,
	2020		2019
Accounts receivable, net	$	(6.5)	$	(16.7)
Deferred revenue	$	10.7	$	9.4
Other liabilities	$	280.9	$	558.6

Other liabilities include up-front payments received from Sanofi for which recognition has been deferred.

The aggregate amount of the estimated consideration under the IO Collaboration related to the Company's obligation that was unsatisfied (or partially unsatisfied) as of December 31, 2020 was $557.5 million. This amount is expected to be recognized over the remaining period in which the Company is obligated to satisfy its obligation in connection with performing development activities.

b. Bayer

Amounts recognized in our Statements of Operations in connection with our Bayer EYLEA collaboration are as follows:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	Bayer collaboration revenue	$	1,107.9	$	1,091.4	$	992.3
Reimbursement for manufacturing of commercial supplies	Bayer collaboration revenue	$	78.2	$	54.2	$	43.8
Reimbursement of development expenses	Reduction of Research and development expense	$	46.7	$	23.0	$	11.2
Regeneron's obligation for its share of Bayer research and development expenses	Research and development expense	$	(35.8)	$	(20.1)	$	(0.5)
Reimbursement of other expenses	Cost of collaboration and contract manufacturing	$	7.4	$	19.0	$	28.9

The Company is party to a license and collaboration agreement with Bayer for the global development and commercialization of EYLEA outside the United States. All agreed-upon EYLEA development expenses incurred by the Company and Bayer are shared equally. The Company is also obligated to use commercially reasonable efforts to supply clinical and commercial bulk product of EYLEA.

Bayer markets EYLEA outside the United States, where, for countries other than Japan, the companies share equally in profits and losses from sales of EYLEA. In Japan, the Company is currently entitled to receive a tiered percentage of between 33.5% and 40.0% of EYLEA net product sales through 2021, and thereafter, the companies will share equally in profits and losses from the sales of EYLEA. Within the United States, the Company is responsible for commercialization of EYLEA and retains exclusive rights to all profits from such commercialization in the United States. The Company is obligated to reimburse Bayer out of its share of the collaboration profits (including the Company's percentage of sales of EYLEA in Japan) for 50% of the agreed-upon development expenses that Bayer has incurred in accordance with a formula based on the amount of development expenses that Bayer has incurred and the Company's share of the collaboration profits, or at a faster rate at the Company's option. The Company's contingent reimbursement obligation to Bayer was approximately $276 million as of December 31, 2020.

The following table summarizes contract balances in connection with our Bayer EYLEA collaboration:


	As of December 31,
	2020		2019
Accounts receivable - other	$	336.2	$	311.6
Deferred revenue	$	99.7	$	123.0

c. Teva

The Company and Teva are parties to a collaboration agreement (the "Teva Collaboration Agreement") to develop and commercialize fasinumab globally, excluding certain Asian countries that are subject to our collaboration agreement with Mitsubishi Tanabe Pharma Corporation. In connection with the Teva Collaboration Agreement, Teva made a $250.0 million non-refundable up-front payment. The Company leads global development activities, and the parties share development costs equally, on an ongoing basis, under a global development plan. The Company is also responsible for the manufacture and supply of fasinumab globally.

Within the United States, the Company will lead commercialization activities, and the parties will share equally in any profits and losses in connection with commercialization of fasinumab. In the territory outside the United States, Teva will lead commercialization activities and the Company will supply product to Teva at a tiered purchase price, which is calculated as a percentage of net sales of the product (subject to adjustment in certain circumstances).

During 2018, the Company achieved a development milestone of $60.0 million. The Company is entitled to receive up to an aggregate of $340.0 million in additional development milestones and up to an aggregate of $1.890 billion in contingent payments upon achievement of specified annual net sales amounts.

At the inception of the Teva Collaboration Agreement, the Company's significant promised goods and services consisted of a license to certain rights and intellectual property and providing research and development services, including the manufacturing of clinical supplies. The Company concluded that the license was not distinct, primarily as a result of (i) Teva being unable to benefit from the license on its own or together with other resources that are readily available as the license provides access to Regeneron's complex and specialized know-how and (ii) the research and development services, including manufacturing in support of such services, were expected to significantly modify the initial license. Therefore, the promised goods and services were considered a combined unit of account. Consequently, the $250.0 million up-front payment and development milestones received from Teva, as described above, have been recorded within other liabilities and included in the transaction price.

Amounts recognized in our Statements of Operations in connection with the Teva Collaboration Agreement are as follows:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Reimbursement of research and development expenses	Reduction of Research and development expense	$	109.4	$	122.9	$	129.5
Amounts recognized in connection with up-front and development milestone payments received	Other operating income	$	47.2	$	82.2	$	113.2

The following table summarizes contract balances in connection with the Teva Collaboration Agreement:


	As of December 31,
	2020		2019
Accounts receivable - other	$	27.7	$	21.2
Other liabilities	$	66.8	$	114.4

Other liabilities include up-front and development milestone payments received from Teva for which recognition has been deferred.

The aggregate amount of the estimated consideration under the Teva Collaboration Agreement related to the Company's obligation that was unsatisfied (or partially unsatisfied) as of December 31, 2020 was $155.9 million. This amount is expected to be recognized over the remaining period in which the Company is obligated to satisfy its obligation in connection with performing development activities.

d. Intellia

In 2016, we entered into a license and collaboration agreement with Intellia Therapeutics, Inc. to advance CRISPR/Cas9 gene-editing technology for in vivo therapeutic development. The parties collaborate to conduct research for the discovery, development, and commercialization of new therapies, in addition to the research and technology development of the CRISPR/Cas9 platform.

Under the terms of the 2016 agreement, the parties agreed to a target selection process, whereby the Company may obtain exclusive rights in up to 10 targets to be chosen by the Company during the collaboration term, subject to various adjustments

and limitations set forth in the agreement. Certain targets that either we or Intellia select pursuant to the target selection process may be subject to a co-development and co-commercialization arrangement at our option or Intellia’s option, as applicable.

In May 2020, we expanded our existing collaboration with Intellia to provide us with rights to develop products for additional in vivo CRISPR/Cas9-based therapeutic targets and for the parties to jointly develop potential products for the treatment of hemophilia A and B. In addition, we also received non-exclusive rights to independently develop and commercialize ex vivo gene edited products. In connection with the agreement, we made a $70.0 million up-front payment, which was recorded to Research and development expense in 2020, and purchased 925,218 shares of Intellia common stock for an aggregate purchase price of $30.0 million. The amount paid in excess of the fair market value of the shares purchased, or $15.0 million, was also recorded to Research and development expense in 2020.

e. U.S. Government

REGEN-COV

In the first quarter of 2020, we announced an expansion of our Other Transaction Agreement ("OTA") with the Biomedical Advanced Research Development Authority ("BARDA"), pursuant to which the U.S. Department of Health and Human Services ("HHS") was obligated to fund certain of our costs incurred for research and development activities related to COVID-19 treatments. In July 2020, we entered into an agreement with entities acting at the direction of BARDA and the U.S. Department of Defense to manufacture and deliver filled and finished drug product of REGEN-COV to the U.S. government. The agreement, as subsequently amended, could result in payments to the Company of up to $465.9 million in the aggregate for bulk manufacturing of the drug substance, as well as fill/finish, storage, and other activities. See Note 2 for REGEN-COV net product sales recognized in connection with this agreement during 2020.

In January 2021, the Company announced an agreement with an entity acting on behalf of the U.S. Department of Defense and HHS to manufacture and deliver additional filled and finished drug product of REGEN-COV to the U.S. government. Pursuant to the agreement, the U.S. government is obligated to purchase all filled and finished doses of drug product delivered by June 30, 2021, and may accept doses during the period from July 1, 2021 through September 30, 2021 at its discretion. The U.S. government will acquire doses at the lowest treatment dose authorized or approved by the FDA for the indication authorized under the EUA, resulting in payments to the Company of up to $2.625 billion in the aggregate. A number of factors may impact available filled and finished supply by June 30, 2021, including manufacturing considerations and authorized dose level.

f. Roche

In August 2020, we entered into a collaboration agreement with Roche to develop, manufacture, and distribute REGEN-COV. We will continue to lead global development activities for REGEN-COV, and the parties will jointly fund certain ongoing studies, as well as any mutually agreed additional new global studies to evaluate further the potential of REGEN-COV in treating or preventing COVID-19. Roche will be responsible for securing regulatory approvals outside the United States, following the initial European Medicines Agency ("EMA") approval (if any), and conducting any additional studies specifically required for approval by regulators outside the United States.

Under the terms of the agreement, each party is obligated to dedicate a certain amount of manufacturing capacity to REGEN-COV each year. We will distribute the product in the United States and Roche will distribute the product outside of the United States. The parties will share gross profits from worldwide sales based on a pre-specified formula, depending on the amount of manufactured product supplied by each party to the market. Any profit sharing will commence after product manufactured by Roche receives regulatory authorization.

During 2020, we recorded $78.5 million of reimbursements received from Roche as a reduction of Research and development expense.

g. Alnylam

In April 2019, the Company and Alnylam Pharmaceuticals, Inc. entered into a global, strategic collaboration to discover, develop, and commercialize RNA interference ("RNAi") therapeutics for a broad range of diseases by addressing therapeutic disease targets expressed in the eye and central nervous system ("CNS"), in addition to a select number of targets expressed in the liver. The collaboration is governed by a Master Collaboration Agreement (the "Master Agreement") (including the form of a License Agreement and a Co-Commercialization Collaboration Agreement). Under the terms of the Master Agreement, we made an up-front payment of $400.0 million to Alnylam, which was recorded in Research and development expense during 2019. For each program, we will provide Alnylam with a specified amount of funding at program initiation and at lead candidate designation, and Alnylam is eligible to receive up to an aggregate of $200.0 million in clinical proof-of-principle milestones for eye or CNS programs.

Under the collaboration, the parties plan to perform discovery research until designation of lead candidates. Following designation of a lead candidate, the parties may further advance such lead candidate under either a License Agreement or a Co-Commercialization Collaboration Agreement structure. The initial target nomination and discovery period is five years (which may under certain situations automatically be extended for up to seven years in the aggregate) (the "Research Term"). In addition, we have an option to extend the Research Term for an additional five-year period for a research extension fee ranging from $200.0 million to $400.0 million; the actual amount of the fee will be determined based on the acceptance of one or more INDs (or their equivalent in certain other countries) for programs in the eye and CNS.

In connection with the collaboration, we and Alnylam also entered into a Stock Purchase Agreement. Pursuant to the terms of the Stock Purchase Agreement, we purchased shares of Alnylam common stock for aggregate cash consideration of $400.0 million.

In August 2019, the parties entered into a Co-Commercialization Collaboration Agreement for a silencing RNA ("siRNA") therapeutic targeting the C5 component of the human complement pathway being developed by Alnylam, with Alnylam as the lead party, and a License Agreement for a combination product consisting of such siRNA therapeutic (cemdisiran) and a fully human monoclonal antibody targeting C5 being developed by us (pozelimab), with us as the licensee. The C5 siRNA Co-Commercialization Collaboration Agreement is consistent with the financial terms contained in the form of the existing Co-Commercialization Collaboration Agreement with Alnylam and the parties will share in development expenses equally. The C5 siRNA License Agreement contains a flat low double-digit royalty payable to Alnylam on our potential future net sales of the combination product only subject to customary reductions, as well as up to $325.0 million in commercial milestones.

h. Other

In addition to the collaboration agreements discussed above, the Company has various other collaboration agreements that are not individually significant to its operating results or financial condition at this time. Pursuant to the terms of those agreements, the Company may be required to pay, or it may receive, additional amounts upon the achievement of various development and commercial milestones which in the aggregate could be significant. The Company may also incur, or get reimbursed for, significant research and development costs if the related product candidate(s) were to advance to late stage clinical trials. In addition, if any products related to these collaborations are approved for sale, the Company may be required to pay, or it may receive, royalties on future sales. The payment or receipt of these amounts, however, is contingent upon the occurrence of various future events.

Marketable Securities

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities as of December 31, 2020 and 2019 consist of both available-for-sale debt securities of investment grade issuers (see below and Note 5) as well as equity securities of publicly traded companies (see Note 5).

The following tables summarize the Company's investments in available-for-sale debt securities:


	Amortized		Unrealized				Fair
As of December 31, 2020	Cost Basis		Gains		Losses		Value
Corporate bonds	$	3,053.0	$	37.5	$	(0.2)	$	3,090.3
U.S. government and government agency obligations	127.6		1.3		—		128.9
Sovereign bonds	65.2		1.1		—		66.3
Commercial paper	276.0		0.1		—		276.1
Certificates of deposit	127.4		0.1		—		127.5
	$	3,649.2	$	40.1	$	(0.2)	$	3,689.1

As of December 31, 2019
Corporate bonds	$	3,960.5	$	27.8	$	(0.2)	$	3,988.1
U.S. government and government agency obligations	54.3		0.2		(0.1)		54.4
Sovereign bonds	26.9		0.4		—		27.3
Commercial paper	92.3		—		—		92.3
Certificates of deposit	72.3		0.1		—		72.4
	$	4,206.3	$	28.5	$	(0.3)	$	4,234.5

The Company classifies its investments in available-for-sale debt securities based on their contractual maturity dates. The available-for-sale debt securities listed as of December 31, 2020 mature at various dates through October 2025. The fair values of available-for-sale debt security investments by contractual maturity consist of the following:


	As of December 31,
	2020		2019
Maturities within one year	$	1,393.3	$	1,596.5
Maturities after one year through five years	2,295.8		2,638.0
	$	3,689.1	$	4,234.5

Unrealized losses of our available-for-sale debt securities that had been in a continuous loss position, for both less than and greater than 12 months, were not material for the years ended December 31, 2020 and 2019.

Realized gains on sales of marketable securities for the year ended December 31, 2020 were $29.0 million and realized gains were not material for the years ended December 31, 2019 and 2018. Realized losses on sales of marketable securities were not material for the years ended December 31, 2020 and 2018 and there were no realized losses for the year ended December 31, 2019.

With respect to marketable securities, for the years ended December 31, 2020, 2019, and 2018, amounts reclassified from Accumulated other comprehensive income (loss) into Other income (expense), net were related to realized gains and losses on sales of available-for-sale debt securities (as described above).

Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

The table below summarizes the Company's assets which are measured at fair value on a recurring basis. The following fair value hierarchy is used to classify assets, based on inputs to valuation techniques utilized to measure fair value:

•Level 1 - Quoted prices in active markets for identical assets

•Level 2 - Significant other observable inputs, such as quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model-based valuations in which significant inputs used are observable

•Level 3 - Significant other unobservable inputs


			Fair Value Measurements at Reporting Date
As of December 31, 2020	Fair Value		Level 1		Level 2
Available-for-sale debt securities:
Corporate bonds	$	3,090.3	—		$	3,090.3
U.S. government and government agency obligations	128.9		—		128.9
Sovereign bonds	66.3		—		66.3
Commercial paper	276.1		—		276.1
Certificates of deposit	127.5		—		127.5
Equity securities (unrestricted)	48.3		$	48.3	—
Equity securities (restricted)	791.5		791.5		—
	$	4,528.9	$	839.8	$	3,689.1

As of December 31, 2019
Available-for-sale debt securities:
Corporate bonds	$	3,988.1	—		$	3,988.1
U.S. government and government agency obligations	54.4		—		54.4
Sovereign bonds	27.3		—		27.3
Commercial paper	92.3		—		92.3
Certificates of deposit	72.4		—		72.4
Equity securities (unrestricted)	61.6		$	61.6	—
Equity securities (restricted)	557.2		557.2		—
	$	4,853.3	$	618.8	$	4,234.5

The Company held certain restricted equity securities as of December 31, 2020 which are subject to transfer restrictions that expire at various dates through 2024.

During the years ended December 31, 2020 and 2019, we recorded $196.0 million and $118.3 million of net unrealized gains, respectively, on equity securities in Other income (expense). During the year ended December 31, 2018, we recorded net unrealized losses on equity securities of $41.9 million in Other income (expense).

In addition to the investments summarized in the table above, as of December 31, 2020 and 2019, the Company had $59.2 million and $55.6 million, respectively, in equity investments that do not have a readily determinable fair value. These investments are recorded within Other noncurrent assets.

The fair value of our long-term debt (see Note 9) was estimated to be $1.958 billion as of December 31, 2020, and was determined based on Level 2 inputs.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Inventories

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

Inventories

Inventories consist of the following:


	As of December 31,
	2020		2019
Raw materials	$	459.4	$	216.3
Work-in-process	904.6		727.7
Finished goods	121.7		70.6
Deferred costs	430.9		400.9
	$	1,916.6	$	1,415.5

Deferred costs represent the costs of product manufactured and shipped to the Company's collaborators for which recognition of revenue has been deferred. For the years ended December 31, 2020, 2019, and 2018, Cost of goods sold included inventory write-downs and reserves of $39.2 million, $73.8 million, and $12.5 million, respectively.

Property, Plant, and Equipment

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, Plant, and Equipment

Property, plant, and equipment consists of the following:


	As of December 31,
	2020		2019
Land	$	241.2	$	230.8
Building and improvements	1,891.1		1,683.4
Leasehold improvements	100.5		97.6
Construction in progress	724.5		644.8
Laboratory equipment	1,038.6		850.7
Computer equipment and software	226.3		183.7
Furniture, office equipment, and other	130.5		121.8
	4,352.7		3,812.8
Less, accumulated depreciation and amortization	(1,131.1)		(922.4)
	$	3,221.6	$	2,890.4

Property, plant, and equipment in the table above includes leased property under the Company's finance lease at its Tarrytown, New York facility. See Note 10.

Depreciation and amortization expense (including as it relates to the Company's finance lease) on property, plant, and equipment amounted to $230.8 million, $205.2 million, and $144.1 million for the years ended December 31, 2020, 2019, and 2018, respectively.

As of December 31, 2020 and 2019, $2.398 billion and $2.118 billion, respectively, of the Company's net property, plant, and equipment was located in the United States and $823.8 million and $772.8 million, respectively, was located in Europe (primarily in Ireland).

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following:


	As of December 31,
	2020		2019
Accrued payroll and related costs	$	465.8	$	344.4
Accrued clinical expenses	283.0		142.7
Accrued sales-related charges, deductions, and royalties	423.9		249.0
Income taxes payable	19.5		49.4
Other accrued expenses and liabilities	329.6		425.9
	$	1,521.8	$	1,211.4

Debt	12 Months Ended
Debt	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt Credit Facility In December 2018, we entered into an agreement with a syndicate of lenders (the "Credit Agreement") which provides for a $750.0 million senior unsecured five-year revolving credit facility (the "Credit Facility"). The Credit Agreement includes an option for us to elect to increase the commitments under the Credit Facility and/or to enter into one or more tranches of term loans in the aggregate principal amount of up to $250.0 million, subject to the consent of the lenders providing the additional commitments or term loans, as applicable, and certain other conditions. Proceeds of the loans under the Credit Facility may be used to finance working capital needs, and for general corporate or other lawful purposes, of Regeneron and its subsidiaries. The Credit Agreement also provides a $50.0 million sublimit for letters of credit. The Credit Agreement includes an option for us to elect to extend the maturity date of the Credit Facility beyond December 2023, subject to the consent of the extending lenders and certain other conditions. Amounts borrowed under the Credit Facility may be prepaid, and the commitments under the Credit Facility may be terminated, at any time without premium or penalty. We had no borrowings outstanding under the Credit Facility as of December 31, 2020. The Credit Agreement contains financial and operating covenants. The Company was in compliance with all covenants of the Credit Facility as of December 31, 2020. Bridge Loan Facility As described in Note 11, in May 2020, we purchased shares of our Common Stock from Sanofi, in connection with Sanofi's secondary offering of our Common Stock held by Sanofi, with a combination of cash on hand, proceeds from the sale of marketable securities, and proceeds from loans under a $1.5 billion senior unsecured 364-day bridge loan facility (the "Bridge Facility"). The loans under the Bridge Facility bore interest at a variable interest rate based on either the London Interbank Offered Rate or the alternate base rate, plus an applicable margin that varied with our debt rating and total leverage ratio. The Bridge Facility was repaid in full during 2020 following the closing of the issuance and sale of the Company's senior notes (as described below). Senior Notes In August 2020, we issued and sold $1.250 billion aggregate principal amount of senior unsecured notes due 2030 (the "2030 Notes") and $750 million aggregate principal amount of senior unsecured notes due 2050 (the "2050 Notes" and, together with the 2030 Notes, the "Notes"). Net proceeds from the issuance and sale of the Notes (after deducting underwriting discounts and offering expenses) were used in part to repay in full the Bridge Facility described above, including accrued interest and related fees and expenses in connection therewith. The underwriting discounts and offering expenses are being amortized as additional interest expense over the period from issuance through maturity. The 2030 Notes accrue interest at the rate of 1.750% per year and will mature on September 15, 2030. The 2050 Notes accrue interest at the rate of 2.800% per year and will mature on September 15, 2050. Interest on each series of Notes is payable semi-annually in arrears on March 15 and September 15 of each year until their respective maturity dates. Interest expense related to the Notes for the year ended December 31, 2020 was $17.6 million. The Notes may be redeemed at the Company’s option at any time at 100% of the principal amount plus accrued and unpaid interest, and, until a specified period before maturity, a specified make-whole amount. The Notes contain a change-of-control provision that, under certain circumstances, may require the Company to offer to repurchase the Notes at a price equal to 101% of the principal amount plus accrued and unpaid interest. The Notes also contain certain limitations on the Company’s ability to incur liens and enter into sale and leaseback transactions, as well as customary events of default.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

See Note 15 for disclosures related to legal contingencies.

a. Leases

We conduct certain of our research, development, and administrative activities at leased facilities. We also lease certain warehouses and vehicles. As described in Note 1, during the first quarter of 2019, we adopted ASC 842, Leases.

Operating leases

Amounts recognized in our Consolidated Balance Sheets and Statements of Operations included in this report associated with operating leases were not material. Operating lease right-of-use assets are included within Other noncurrent assets, and lease liabilities are included in Accrued expenses and other current liabilities and Other noncurrent liabilities.

Finance leases

In March 2017, we entered into a Participation Agreement with BA Leasing BSC, LLC, an affiliate of Banc of America Leasing & Capital LLC ("BAL"), as lessor, and a syndicate of lenders (collectively, the "Lease Participants"). In March 2017, we also entered into a Lease and Remedies Agreement with BAL, pursuant to which we have leased laboratory and office facilities in Tarrytown, New York (the "Facility") for a five-year term ending in March 2022. The Participation Agreement, the Lease and Remedies Agreement, and certain other related agreements were amended and restated in May 2019, among other things, to revise certain covenants, representations and warranties, and events of default to be substantially similar to those set forth in the agreement governing the Company's revolving credit facility (as so amended and restated, the "Participation Agreement" and the "Lease," respectively). The Lease requires us to pay all maintenance, insurance, taxes, and other costs arising out of the use of the Facility. We are also required to make monthly payments of basic rent during the term of the Lease in an amount equal to a variable rate per annum based on the one-month LIBOR, plus an applicable margin that varies with our debt rating and total leverage ratio. The Participation Agreement and the Lease include an option for us to elect to extend the maturity date of the Participation Agreement and the term of the Lease for an additional five-year period, subject to the consent of all the Lease Participants and certain other conditions. We also have the option prior to the end of the term of the Lease to (a) purchase the Facility by paying an amount equal to the outstanding principal amount of the Lease Participants' advances under the Participation Agreement, all accrued and unpaid interest and yield thereon, and all other outstanding amounts under the Participation Agreement, the Lease, and certain related documents or (b) sell the Facility to a third party on behalf of BAL. The advances under the Participation Agreement mature, and all amounts outstanding thereunder will become due and payable in full, at the end of the term of the Lease.

Prior to January 1, 2019, for certain of the premises under the Lease we were deemed, in substance, to be the owner of the buildings (collectively, the "Build-to-Suit Buildings"). Upon the adoption of ASC 842, the classification of the Build-to-Suit Buildings, for which the construction period had been completed, was reassessed and, consequently, they were derecognized and recognized as a finance lease. These premises, along with the other premises under the Lease, are classified as a finance lease as we have the option to purchase the Facility under terms that make it reasonably certain to be exercised.

The agreements governing the Lease financing contain financial and operating covenants. The Company was in compliance with all such covenants as of December 31, 2020.

Amounts recognized in the Consolidated Balance Sheet related to the Lease are included in the table below. Other than the Lease described above, we had no leases accounted for as finance leases as of December 31, 2020 and 2019.


		As of December 31,
	Classification	2020		2019
Finance lease right-of-use assets	Property, plant, and equipment, net(1)	$	645.7	$	660.1
Finance lease liabilities	Finance lease liabilities (noncurrent)	$	717.2	$	713.9

(1) Finance lease right-of-use assets are recorded net of accumulated amortization of $90.5 million and $76.1 million as of December 31, 2020 and 2019, respectively.

Finance lease costs consist of the following:


	Year Ended December 31,
	2020		2019
Amortization of right-of-use assets	$	14.4	$	14.4
Interest on lease liabilities	15.7		27.6
	$	30.1	$	42.0

Other information related to our finance lease includes the following:


	As of December 31,
	2020	2019
Remaining lease term (in years)	1.17	2.17
Discount rate	1.66%	3.05%

Supplemental information

The following is a maturity analysis of our finance lease liabilities:


	As of December 31, 2020
2021	$	12.1
2022	723.1
2023	—
2024	—
2025	—
Thereafter	—
Total undiscounted lease payments	735.2
Imputed interest	(15.1)
Debt financing costs	(2.9)
Total lease liabilities	$	717.2

b. Research Collaboration and Licensing Agreements

As part of our research and development efforts, we enter into research collaboration and licensing agreements with other companies, universities, and other organizations. These agreements contain varying terms and provisions which include fees to be paid by the Company, services to be provided, and license rights to certain proprietary technology developed under the agreements. Some of these agreements may require the Company to pay additional amounts upon the achievement of various development and commercial milestones, contingent upon the occurrence of various future events. Additionally, we have in-licensed patent and/or technology pursuant to agreements which contain provisions that require the Company to pay royalties, as defined, at rates that range from 0.5% to 11.5%, in the event the Company sells or licenses any proprietary products developed under the respective agreements. The Company also has contingent reimbursement obligations to its collaborators Sanofi and Bayer out of the respective collaboration's profits, if they are sufficient for that purpose. See Note 3 for a more detailed description of collaboration, license, and other agreements.

For the years ended December 31, 2020, 2019, and 2018, the Company recorded royalty expense (net of reimbursements from collaborators, as applicable) in Cost of goods sold and Cost of collaboration and contract manufacturing of $56.5 million, $47.0 million, and $30.1 million, respectively, based on product sales of commercial products under various licensing agreements.

Stockholders' Equity

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Stockholders' Equity

The Company's Restated Certificate of Incorporation, as amended, provides for the issuance of up to 40 million shares of Class A Stock, par value $0.001 per share, and 320 million shares of Common Stock, par value $0.001 per share. Shares of Class A Stock are convertible, at any time, at the option of the holder into shares of Common Stock on a share-for-share basis. Holders of Class A Stock have rights and privileges identical to Common Stockholders except that each share of Class A is entitled to ten votes per share, while each share of Common Stock is entitled to one vote per share. Class A Stock may only be transferred to specified Permitted Transferees, as defined. Under the Company's Restated Certificate of Incorporation, the Company's board of directors is authorized to issue up to 30 million shares of Preferred Stock, in series, with rights, privileges, and qualifications of each series determined by the board of directors.

Share Repurchase Program

In November 2019, our board of directors authorized a share repurchase program to repurchase up to $1.0 billion of our Common Stock. The share repurchase program permitted the Company to effect repurchases through a variety of methods, including open-market transactions (including pursuant to a trading plan adopted in accordance with Rule 10b5-1 of the Exchange Act), privately negotiated transactions, accelerated share repurchases, block trades, and other transactions in compliance with Rule 10b-18 of the Exchange Act. As of December 31, 2020, the Company had repurchased the entire $1.0 billion it was authorized to repurchase under the program.

The table below summarizes the shares of our Common Stock we repurchased under the program and the cost of the shares received, which were recorded as Treasury Stock.


	Year Ended December 31,
	2020		2019
Number of shares repurchased	1,605,582		722,596
Total cost of shares received	$	746.0	$	254.0

In January 2021, our board of directors authorized a new share repurchase program to repurchase up to $1.5 billion of our Common Stock. The share repurchase program was approved under terms substantially similar to the November 2019 share repurchase program described above.

Arrangements with Sanofi

In 2007, Sanofi purchased 12 million newly issued, unregistered shares of the Company's Common Stock. As a condition to the closing of this transaction, Sanofi entered into an investor agreement, as amended and restated, with the Company. Under the amended and restated investor agreement, Sanofi agreed not to dispose of any shares of the Company's Common Stock beneficially owned by Sanofi from time to time until December 20, 2020 (subject to the limited waiver described below).

Further, pursuant to the amended and restated investor agreement, Sanofi is bound by certain "standstill" provisions, which contractually prohibit Sanofi from seeking to directly or indirectly exert control of the Company or acquiring more than 30% of

the outstanding shares of the Company's Class A Stock and Common Stock (taken together). This prohibition will remain in place until the earliest of (i) the later of the fifth anniversaries of the expiration or earlier termination of the Company's License and Collaboration Agreement with Sanofi and the Company's ZALTRAP Agreement with Sanofi, each as amended, and (ii) other specified events. Sanofi has also agreed to vote as recommended by the Company's board of directors, except that it may elect to vote proportionally with the votes cast by all of the Company's other shareholders with respect to certain change-of-control transactions, and to vote in its sole discretion with respect to liquidation or dissolution, stock issuances equal to or exceeding 20% of the outstanding shares or voting rights of the Company's Class A Stock and Common Stock (taken together), and new equity compensation plans or amendments if not materially consistent with the Company's historical equity compensation practices. The rights and restrictions under the investor agreement are subject to termination upon the occurrence of certain events and have been amended in connection with the Secondary Offering and the Stock Purchase (each as defined below).

As described in Note 3, effective January 2018, we and Sanofi entered into a Letter Agreement, which, among other things, amended certain provisions of the amended and restated investor agreement. Pursuant to the Letter Agreement, we granted Sanofi a limited waiver of the lock-up obligations under the investor agreement in order to allow Sanofi to satisfy in whole or in part its funding obligations with respect to Libtayo development costs and/or Dupilumab/Itepekimab Eligible Investments for quarterly periods ending on September 30, 2020 by selling our Common Stock directly or indirectly owned by Sanofi. The table below summarizes the shares of our Common Stock Sanofi elected to sell, and we elected to purchase, to satisfy Sanofi's funding obligations and the cost of the shares received, which were recorded as Treasury Stock.


	As of December 31,
	2020		2019		2018
Libtayo:
Number of shares purchased (by issuing a credit towards the amount owed by Sanofi)	77,677		210,733		215,387
Total cost of shares received	$	41.7	$	73.3	$	75.8

Dupilumab/Itepekimab:
Number of shares purchased (in cash)	171,471		93,286		10,766
Total cost of shares received	$	93.3	$	29.4	$	4.4

In May 2020, a secondary offering of 13,014,646 shares of our Common Stock (the "Secondary Offering") held by Sanofi was completed. In connection with the Secondary Offering, we also purchased 9,806,805 shares directly from Sanofi for an aggregate purchase amount of $5 billion (the "Stock Purchase"). See Note 9 for additional information. As a result of the Secondary Offering and the Stock Purchase, Sanofi disposed of all of its shares of our Common Stock, other than 400,000 shares that it retained as of the closing of the Secondary Offering and the Stock Purchase (a portion of which Sanofi has used for the funding of certain development costs described above).

In May 2020, the Company entered into an amendment to the amended and restated investor agreement, which provides, among other things, that following the Secondary Offering and Share Purchase, (1) the “standstill” provisions, which contractually prohibit Sanofi from seeking to directly or indirectly exert control of the Company, continue to apply pursuant to their terms; (2) the voting commitments contained in the investor agreement continue to apply to the shares of Common Stock held by Sanofi and its affiliates following the secondary offering and stock repurchase, for so long as such shares are held by them; and (3) the lock-up restrictions in the investor agreement continued to apply to the shares of Common Stock held by Sanofi following the Secondary Offering and Stock Purchase until December 20, 2020 (except those shares which could be used to satisfy certain funding obligations of Sanofi).

Arrangements with Other Collaborators

In connection with the Company's license and collaboration agreements with Bayer for the joint development and commercialization outside the United States of antibody product candidates to PDGFR-beta and Ang2, Bayer is bound by certain "standstill" provisions, which contractually prohibit Bayer from seeking to influence the control of the Company or acquiring more than 20% of the Company's outstanding shares of Class A Stock and Common Stock (taken together). With respect to each of these agreements, this prohibition will remain in place until the earliest of (i) the fifth anniversary of the

termination of the agreement (which, in the case of the PDGFR-beta license and collaboration agreement, occurred on July 31, 2017, and, in the case of the Ang2 agreement, occurred on November 1, 2018) or (ii) other specified events.

Further, pursuant to the 2016 Teva Collaboration Agreement, Teva and its affiliates are bound by certain "standstill" provisions, which contractually prohibit them from seeking to directly or indirectly exert control of the Company or acquiring more than 5% of the Company's Class A Stock and Common Stock (taken together). This prohibition will remain in place until the earliest of (i) the fifth anniversary of the expiration or earlier termination of the agreement or (ii) other specified events.

Long-Term Incentive Plans

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Long-Term Incentive Plans

The Company has used long-term incentive plans for the purpose of granting equity awards to employees of the Company, including officers, and nonemployees, including nonemployee members of the Company's board of directors (collectively, "Participants"). The Participants may receive awards as determined by a committee of independent members of the Company's board of directors or, to the extent authorized by such committee with respect to certain Participants, a duly authorized employee (collectively, the "Committee"). The incentive plan currently used by the Company is the Second Amended and Restated Regeneron Pharmaceuticals, Inc. 2014 Long-Term Incentive Plan (the "Second Amended and Restated 2014 Incentive Plan"). It was most recently adopted and approved by the Company's shareholders in 2020, at which time the Company registered an additional 12,000,000 shares of Common Stock for issuance thereunder. As of the most recent shareholder approval date, the Second Amended and Restated 2014 Incentive Plan provided for the issuance of up to 22,269,970 shares of Common Stock in respect of awards. In addition, upon expiration, forfeiture, surrender, exchange, cancellation, or termination of any award previously granted under the Amended and Restated Regeneron Pharmaceuticals, Inc. 2014 Long-Term Incentive Plan (the "Amended and Restated 2014 Incentive Plan"), the Regeneron Pharmaceuticals, Inc. 2014 Long-Term Incentive Plan (the "Original 2014 Incentive Plan"), or the Second Amended and Restated 2000 Long-Term Incentive Plan (the "2000 Incentive Plan"), any shares subject to such award are added to the pool of shares available for grant under the Second Amended and Restated 2014 Incentive Plan.

The awards that may be made under the Second Amended and Restated 2014 Incentive Plan include: (a) incentive stock options and nonqualified stock options, (b) shares of restricted stock, (c) shares of phantom stock (also referred to as restricted stock units, which may be time- or performance-based), and (d) other awards. Any award granted may (but is not required to) be subject to vesting based on the attainment by the Company of performance goals pre-established by the Committee.

Stock option awards grant Participants the right to purchase shares of Common Stock at prices determined by the Committee, with exercise prices that are equal to or greater than the average of the high and low market prices of the Company's Common Stock on the date of grant (the "Market Price"). Options vest over a period of time determined by the Committee, generally on a pro rata basis over a three- to four-year period. The Committee also determines the expiration date of each option. The maximum term of options that have been awarded under the 2000 Incentive Plan, the Original 2014 Incentive Plan, the Amended and Restated 2014 Incentive Plan, and the Second Amended and Restated 2014 Incentive Plan (collectively, the "Incentive Plans") is ten years.

Restricted stock awards grant Participants shares of restricted Common Stock or allow Participants to purchase such shares at a price determined by the Committee. Such shares are nontransferable for a period determined by the Committee ("vesting period"). Should employment terminate, as specified in the Incentive Plans, except as determined by the Committee in its discretion and subject to the applicable Incentive Plan documents, the ownership of any unvested restricted stock will be transferred to the Company.

Phantom stock awards provide the Participant the right to receive Common Stock or an amount of cash based on the value of the Common Stock at a future date. The award is subject to such restrictions, if any, as the Committee may impose at the date of grant or thereafter, including a specified period of employment or the achievement of performance goals. Time-based restricted stock units and performance-based restricted stock units are each a type of phantom stock award permitted under the Second Amended and Restated 2014 Incentive Plan.

The Incentive Plans contain provisions that allow for the Committee to provide for the immediate vesting of awards upon a change in control of the Company, as defined in the Incentive Plans.

As of December 31, 2020, there were 18,916,095 shares available for future grants under the Second Amended and Restated 2014 Incentive Plan. No additional awards may be made under the 2000 Incentive Plan, the Original 2014 Incentive Plan, or the Amended and Restated 2014 Incentive Plan.

a. Stock Options

Transactions involving stock option awards during 2020 under the Company's Incentive Plans are summarized in the table below.


		Number of Shares	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Intrinsic Value
Outstanding as of December 31, 2019		28,609,277	$	337.24
2020:	Granted	2,850,590	$	492.60
	Forfeited	(562,629)	$	379.02
	Expired	(56,282)	$	473.77
	Exercised	(9,139,287)	$	281.90
Outstanding as of December 31, 2020		21,701,669	$	379.51	6.34	$	2,347.4

Vested and expected to vest as of December 31, 2020		20,764,534	$	377.23	6.22	$	2,294.1

Exercisable as of December 31, 2020		13,648,899	$	357.65	4.96	$	1,799.1

The Company satisfies stock option exercises with newly issued shares of the Company's Common Stock. The total intrinsic value of stock options exercised during 2020, 2019, and 2018 was $2.251 billion, $558.9 million, and $510.6 million, respectively. The intrinsic value represents the amount by which the market price of the underlying stock exceeds the exercise price of an option.

The table below summarizes the weighted-average exercise prices and weighted-average grant-date fair values of options issued during the years ended December 31, 2020, 2019, and 2018.


	Number of Options Granted	Weighted-Average Exercise Price		Weighted-Average Fair Value
2020:
Exercise price equal to Market Price	2,850,590	$	492.60	$	126.50
2019:
Exercise price equal to Market Price	3,271,222	$	366.65	$	100.80
2018:
Exercise price equal to Market Price	4,665,320	$	378.51	$	114.39

For the years ended December 31, 2020, 2019, and 2018, the Company recognized $329.5 million, $422.8 million, and $421.8 million, respectively, of non-cash stock-based compensation expense related to stock option awards (net of amounts capitalized as inventory of $8.3 million, $2.4 million, and $17.1 million, respectively). As of December 31, 2020, there was $491.5 million of stock-based compensation cost related to outstanding stock options, net of estimated forfeitures, which had not yet been recognized. The Company expects to recognize this compensation cost over a weighted-average period of 1.8 years.

Fair Value Assumptions:

The following table summarizes the weighted average values of the assumptions used in computing the fair value of option grants during 2020, 2019, and 2018.


	2020		2019		2018
Expected volatility	28	%	28	%	29	%
Expected lives from grant date	5.0 years		5.0 years		4.9 years
Expected dividend yield	0	%	0	%	0	%
Risk-free interest rate	0.47	%	1.74	%	2.69	%

Expected volatility has been estimated based on actual movements in the Company's stock price over the most recent historical periods equivalent to the options' expected lives. Expected lives are principally based on the Company's historical exercise experience with previously issued employee and board of directors' option grants. The expected dividend yield is zero as the Company has never paid dividends and does not currently anticipate paying any in the foreseeable future. The risk-free interest rates are based on quoted U.S. Treasury rates for securities with maturities approximating the options' expected lives.

b. Restricted Stock Awards and Time-Based Restricted Stock Units

A summary of the Company's activity related to restricted stock awards and time-based restricted stock units (excluding performance-based restricted stock units, which are detailed further below) (collectively, "restricted stock") during 2020 is summarized below.


		Number of Shares/Units	Weighted-Average Grant Date Fair Value
Balance as of December 31, 2019		1,102,390	$	377.32
2020:	Granted	646,844	$	496.44
	Vested	(15,630)	$	526.62
	Forfeited/Cancelled	(46,061)	$	377.85
Balance as of December 31, 2020		1,687,543	$	421.58

The Company recognized non-cash stock-based compensation expense related to restricted stock of $102.5 million, $29.7 million, and $5.6 million in 2020, 2019, and 2018, respectively (net of amounts capitalized as inventory, which were not material for each of the three years). As of December 31, 2020, there was $425.5 million of stock-based compensation cost related to unvested restricted stock which had not yet been recognized. The Company expects to recognize this compensation cost over a weighted-average period of 2.7 years.

c. Performance-based Restricted Stock Units

Performance-based restricted stock units ("PSUs") have been granted to certain executive officers of the Company. The PSUs will be earned based upon the achievement of predetermined, cumulative total shareholder return goals with respect to the Company's Common Stock price over a specified (generally five-year) period beginning on the grant date. The number of PSUs granted shown in the table below represents the maximum number of units that are eligible to be earned. Depending on the terms of the PSUs and the outcome of the performance goals, a recipient may ultimately earn 0% to 250% (as specified for each PSU grant) of the target number of PSUs granted. A summary of the Company's activity related to PSUs during 2020 is summarized below.


		Number of Shares/Units	Weighted-Average Grant Date Fair Value
Balance as of December 31, 2019		59,396	$	198.10
2020:	Granted	1,240,540	$	209.59
	Vested	—	—
	Forfeited/Cancelled	—	—
Balance as of December 31, 2020		1,299,936	$	209.06

The Company did not recognize non-cash stock-based compensation expense related to PSUs in 2020 (as PSUs granted in 2020 were granted on December 31, 2020 and will be expensed over the vesting period). The Company recognized non-cash stock-based compensation expense related to PSUs of $11.7 million in 2019 (net of amounts capitalized as inventory, which were not material). PSUs were not granted during 2018. As of December 31, 2020, there was $260.0 million of stock-based compensation cost related to unvested PSUs which had not yet been recognized. The Company expects to recognize this compensation cost on a straight-line basis over a period of 5.0 years.

Fair Value Assumptions:

The following table summarizes the weighted average values of the assumptions used in computing the fair value of PSUs during 2020 and 2019.


	2020	2019
Expected volatility	35%	33%
Expected dividend yield	0%	0%
Risk-free interest rate	0.36%	1.63%

Employee Savings Plans	12 Months Ended
Employee Savings Plans	Dec. 31, 2020
Retirement Benefits [Abstract]
Employee Savings Plans	Employee Savings Plans The Company maintains the Regeneron Pharmaceuticals, Inc. 401(k) Savings Plan, as amended and restated (the "Savings Plan"). The terms of the Savings Plan allow U.S. employees (as defined by the Savings Plan) to contribute to the Savings Plan a percentage of their compensation. In addition, the Company may make discretionary contributions ("Contribution"), as defined, to the accounts of participants under the Savings Plan. The Company recognized $44.7 million, $38.1 million, and $27.0 million of Contribution expense in 2020, 2019, and 2018, respectively. The Company also maintains additional employee savings plans outside of the United States, which cover eligible employees. Expenses recognized by the Company related to contributions to such plans were not material during 2020, 2019, and 2018.

- Definition

The entire disclosure for retirement benefits.

+ References

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+ Details

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

The Company is subject to U.S. federal, state, and foreign income taxes. Components of income before income taxes consist of the following:


	Year Ended December 31,
	2020		2019		2018
United States	$	2,442.3	$	2,011.2	$	2,151.7
Foreign	1,368.1		417.9		401.8
	$	3,810.4	$	2,429.1	$	2,553.5

Components of income tax expense consist of the following:


	Year Ended December 31,
	2020		2019		2018
Current:
Federal	$	199.0	$	444.6	$	223.7
State	1.2		1.9		4.8
Foreign	21.4		(2.6)		20.6
Total current tax expense	221.6		443.9		249.1
Deferred:
Federal	109.0		(132.0)		687.6
State	(2.0)		(1.7)		(1.9)
Foreign	(31.4)		3.1		(825.7)
Total deferred tax (benefit) expense	75.6		(130.6)		(140.0)
	$	297.2	$	313.3	$	109.1

A reconciliation of the U.S. statutory income tax rate to the Company's effective income tax rate is as follows:


	Year Ended December 31,
	2020		2019		2018
U.S. federal statutory tax rate	21.0	%	21.0	%	21.0	%
Stock-based compensation	(7.6)		(2.5)		(2.5)
Income tax credits	(2.8)		(4.6)		(2.6)
Taxation of non-U.S. operations	(1.8)		(1.0)		(1.9)
Sale of non-inventory related assets between foreign subsidiaries	(0.8)		—		(6.3)
Foreign-derived intangible income deduction	—		(1.6)		(1.0)
Non-deductible Branded Prescription Drug Fee	0.5		0.7		0.6
Impact of change in U.S. corporate tax rate (the Act)	—		—		(2.7)
Other permanent differences	(0.7)		0.9		(0.3)
Effective income tax rate	7.8	%	12.9	%	4.3	%

In December 2017, the bill known as the "Tax Cuts and Jobs Act" (the "Act") was signed into law. The Act, which became effective with respect to most of its provisions as of January 1, 2018, significantly revised U.S. corporate income tax laws by, among other things, reducing the U.S. federal corporate income tax rate from 35% to 21%. As a result of the Act being signed into law, the Company recognized a provisional charge in the fourth quarter of 2017 related to the re-measurement of its U.S. net deferred tax assets at the lower enacted corporate tax rate, and, during 2018, we recorded an income tax benefit of $68.0 million as a final adjustment to the provisional amount recorded as of December 31, 2017, which was partly attributable to our election to record deferred tax assets and liabilities for expected amounts of GILTI inclusions.

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company's deferred tax assets and liabilities are as follows:


	As of December 31,
	2020		2019
Deferred tax assets:
Deferred compensation	$	436.6	$	519.7
Fixed assets and intangible assets	140.5		192.0
Accrued expenses	139.8		75.9
Deferred revenue	44.6		22.0
Total deferred tax assets	761.5		809.6
Valuation allowance	—		(7.0)
Deferred tax assets, net of valuation allowance	761.5		802.6

Deferred tax liabilities:
Other	(42.8)		(11.2)
Net deferred tax assets	$	718.7	$	791.4

The Company's federal income tax returns for 2015 through 2019 remain open to examination by the IRS. The Company's 2015 and 2016 federal income tax returns are currently under audit by the IRS. In general, the Company's state income tax returns from 2016 to 2019 remain open to examination. The Company’s Commonwealth of Pennsylvania returns for 2015 through 2019 are currently under audit by the Commonwealth. The United States and many states generally have statutes of limitation ranging from 3 to 5 years; however, those statutes could be extended due to the Company's tax credit carryforward position. In general, tax authorities have the ability to review income tax returns in which the statute of limitation has previously expired to adjust the tax credits generated in those years.

The following table reconciles the beginning and ending amounts of unrecognized tax benefits. The amount of unrecognized tax benefits that, if settled, would impact the effective tax rate is $267.0 million, $210.8 million, and $189.5 million as of December 31, 2020, 2019, and 2018, respectively.


	2020		2019		2018
Balance as of January 1	$	210.8	$	189.5	$	146.2
Gross increases related to current year tax positions	76.6		37.9		51.4
Gross increases (decreases) related to prior year tax positions	7.2		(7.2)		5.6
Gross decreases due to settlements and lapse of statutes of limitations	(27.6)		(9.4)		(13.7)
Balance as of December 31	$	267.0	$	210.8	$	189.5

In 2020, 2019 and 2018, the increases in unrecognized tax benefits primarily related to the Company's calculation of certain tax credits and other items related to the Company's international operations.

During 2020, 2019, and 2018, interest expense related to unrecognized tax benefits recorded by the Company was not material. The Company believes it is reasonably possible that its unrecognized tax benefits as of December 31, 2020 may decrease within

the next twelve months, and, as a result, positively impact our effective tax rate, as a result of expected settlement of audits and statute of limitation lapses.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Legal Matters	12 Months Ended
Legal Matters	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Legal Matters	Legal Matters From time to time, the Company is a party to legal proceedings in the course of the Company's business. Costs associated with the Company's involvement in legal proceedings are expensed as incurred. The outcome of any such proceedings, regardless of the merits, is inherently uncertain. The Company recognizes accruals for loss contingencies associated with such proceedings when it is probable that a liability will be incurred and the amount of loss can be reasonably estimated. As of December 31, 2020 and 2019, the Company had accruals for loss contingencies of $9.6 million and $100.0 million, respectively. If the Company were unable to prevail in any such proceedings, its consolidated financial position, results of operations, and future cash flows may be materially impacted. Proceedings Relating to '287 Patent and '163 Patent The Company is a party to patent infringement litigation initiated by the Company involving its European Patent No. 1,360,287 (the "'287 Patent") and its European Patent No. 2,264,163 (the "'163 Patent"). Each of these patents concerns genetically engineered mice capable of producing chimeric antibodies that are part human and part mouse. Chimeric antibody sequences can be used to produce high-affinity fully human monoclonal antibodies. In these proceedings, the Company claims infringement of several claims of the '287 Patent and the '163 Patent (as applicable), and seeks, among other types of relief, an injunction and an account of profits in connection with the defendants' infringing acts, which may include, among other things, the making, use, keeping, sale, or offer for sale of genetically engineered mice (or certain cells from which they are derived) that infringe one or more claims of the '287 Patent and the '163 Patent (as applicable). On September 25, 2013, the Company commenced patent infringement litigation against Kymab Ltd in the English High Court of Justice, Chancery Division, Patents Court, in London, asserting the '287 Patent and '163 Patent. Following a trial to adjudicate the claims of infringement and counterclaims of invalidity of the '287 Patent and the '163 Patent, the court issued a final judgment on February 1, 2016, finding that the asserted claims of the '287 and '163 Patents are novel, not obvious, and infringed by Kymab's genetically engineered mice. However, the court invalidated the '287 and '163 Patents on the ground of insufficiency. On appeal, the Court of Appeal (Civil Division of England and Wales) reversed the English High Court's decision and held that the '287 Patent and '163 Patent are both valid and infringed by Kymab and subsequently issued a final order, which enjoined Kymab from infringing the '287 Patent and '163 Patent (subject to certain exceptions) and required Kymab to destroy or deliver to a third party all products and antibodies and cells engineered to produce antibodies which infringe the '287 Patent and '163 Patent (subject to certain exceptions). On June 24, 2020, the Supreme Court of the United Kingdom overturned the decision of the Court of Appeal on validity and held that the '287 and '163 Patents are each invalid on the ground of insufficiency. Proceedings Relating to Praluent (alirocumab) Injection As described in greater detail below, the Company is currently a party to patent infringement actions initiated by Amgen Inc. (and/or its affiliated entities) against the Company and/or Sanofi (and/or the Company's and Sanofi's respective affiliated entities) in a number of jurisdictions relating to Praluent. See Note 3 for a description of the Company's and Sanofi's arrangement regarding the costs resulting from or associated with such actions. United States In the United States, Amgen has asserted claims of U.S. Patent Nos. 8,829,165 (the "'165 Patent") and 8,859,741 (the "'741 Patent"), and seeks a permanent injunction to prevent the Company and the Sanofi defendants from commercial manufacturing, using, offering to sell, or selling within the United States (as well as importing into the United States) (collectively, "Commercializing") Praluent. Amgen also seeks a judgment of patent infringement of the asserted patents, monetary damages (together with interest), costs and expenses of the lawsuits, and attorneys' fees. As described in greater detail under "Second Jury Trial and Appeal" below, the parties to this litigation are currently awaiting a decision by the Federal Circuit (as defined below) on Amgen's appeal. First Jury Trial and Appeal. The first jury trial in this litigation (the "First Trial") was held in the United States District Court for the District of Delaware (the "District Court") from March 8 to March 16, 2016. During the course of the First Trial, the District Court ruled as a matter of law in favor of Amgen that the asserted patent claims were not obvious, and in favor of the Company and the Sanofi defendants that there was no willful infringement of the asserted patent claims by the Company or the Sanofi defendants. On March 16, 2016, the jury returned a verdict in favor of Amgen in the First Trial, finding that the asserted claims of the '165 and '741 Patents were not invalid based on either a lack of written description or a lack of enablement. On October 5, 2017, the United States Court of Appeals for the Federal Circuit (the "Federal Circuit") reversed in part the District Court's decision and remanded for a new trial on the issues of written description and enablement. In addition, it affirmed the District Court's ruling that Amgen's patents were not obvious. Second Jury Trial and Appeal. On January 3, 2019, the District Court held oral argument in the remanded proceedings on the Company and the Sanofi defendants' motion for judgment on the pleadings regarding Amgen's willful infringement claim. On January 18, 2019, the District Court entered an order (i) denying the Company and the Sanofi defendants' motion for summary judgment on validity, (ii) denying Amgen's motion for partial summary judgment on estoppel, and (iii) granting the Company and the Sanofi defendants' cross-motion for summary judgment on estoppel. On February 8, 2019, the District Court granted the Company and the Sanofi defendants' motion for judgment on the pleadings, thereby dismissing Amgen's claim of willful infringement. The second jury trial in this litigation (the "Second Trial") was held before the District Court in February 2019 to determine the validity of Amgen's asserted patent claims. On February 25, 2019, the jury returned a verdict in the Second Trial generally in favor of Amgen, finding that two claims of the '165 Patent and one claim of the '741 Patent were not invalid. The jury also found that two claims of the '165 Patent were invalid for lack of adequate written description while rejecting the lack of enablement challenges to those two claims. On August 28, 2019, the District Court ruled as a matter of law that Amgen's asserted patent claims are invalid based on lack of enablement. The District Court also conditionally denied the Company and the Sanofi defendants' motion for a new trial. On October 23, 2019, Amgen filed a notice of appeal of the District Court's decision with the Federal Circuit. An oral hearing before the Federal Circuit was held on December 9, 2020. Injunctive Relief Proceedings. On March 18, 2019, Amgen filed a renewed motion for a permanent injunction to prohibit the Company and the Sanofi defendants from Commercializing Praluent in the United States (a "Permanent Injunction"), and an oral hearing on this motion was held in June 2019. Previously, the Federal Circuit stayed and then vacated a Permanent Injunction granted by the District Court in connection with the First Trial. On August 28, 2019, the District Court dismissed as moot Amgen's renewed motion for a Permanent Injunction. Europe Amgen has asserted European Patent No. 2,215,124 (the "'124 Patent"), which pertains to PCSK9 monoclonal antibodies, in the countries in Europe discussed below. As described in greater detail under "EPO Proceedings" below, in October 2020 the '124 Patent claims directed to compositions of matter and medical use were ruled invalid by the Technical Board of Appeal (the "TBA") of the European Patent Office (the "EPO"). This decision, subject to any review by the EPO Enlarged Board of Appeal, has impacted or will impact each of the infringement proceedings based on the '124 Patent discussed below. EPO Proceedings. The '124 Patent was subject to opposition proceedings in the EPO seeking to invalidate certain of its claims, which were initiated by Sanofi on February 24, 2016 and, separately, by the Company, Sanofi, and several other opponents on November 24, 2016. On December 13, 2017, the Opposition Division of the EPO issued a preliminary, non-binding opinion (the "Preliminary Opinion") regarding the validity of the '124 Patent, indicating that it currently considers the claims of a new request filed by Amgen in response to the opposition to satisfy the requirements for patentability. An oral hearing on the oppositions against the '124 Patent was held on November 28–30, 2018, at which the Opposition Division upheld the validity of the '124 Patent's claims in amended form. The Company and Sanofi filed notices of appeal to the TBA on November 30, 2018. An oral hearing before the TBA was held on October 28–29, 2020, at which the TBA ruled that the '124 Patent claims directed to compositions of matter and medical use were invalid based on a lack of inventive step. United Kingdom. On July 25, 2016, Amgen filed a lawsuit against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi-Synthelabo Limited, Aventis Pharma Limited, Sanofi Winthrop Industrie S.A., and Sanofi-Aventis Deutschland GmbH in the English High Court of Justice, Chancery Division, Patents Court, in London, seeking a declaration of infringement of the '124 Patent by Praluent. The lawsuit also seeks a permanent injunction, damages, an accounting of profits, and costs and interest. On February 8, 2017, the court temporarily stayed this litigation on terms mutually agreed by the parties. On October 22, 2020, the court lifted the stay upon application by the Company and the Sanofi defendants, and the case will proceed in due course. Germany. On July 25, 2016, Amgen filed a lawsuit for infringement of the '124 Patent against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi Winthrop Industrie S.A., and Sanofi-Aventis Deutschland GmbH in the Regional Court of Düsseldorf, Germany (the "Düsseldorf Regional Court"), seeking a permanent injunction, an accounting of marketing activities, a recall of Praluent and its removal from distribution channels, and damages. On November 14, 2017, the Düsseldorf Regional Court issued a decision staying the infringement proceedings until a decision of the Opposition Division of the EPO concerning the pending opposition filed by the Company, Sanofi, and several other opponents against the '124 Patent (as discussed above). Following Amgen's request to reopen the proceedings in light of the issuance of the Preliminary Opinion, the Düsseldorf Regional Court held an oral hearing on September 11, 2018 and ruled on December 10, 2018 that the infringement proceedings would be reopened. On July 11, 2019, the Düsseldorf Regional Court found that Praluent infringes the '124 Patent and granted an injunction prohibiting the Company and Sanofi's manufacture, sale, and marketing of Praluent in Germany (the "July 11 Decision"). Amgen subsequently enforced the injunction and, as a result, commercialization of Praluent in Germany was discontinued. On July 12, 2019, the Company and Sanofi appealed the July 11 Decision to the Higher Regional Court of Düsseldorf (the "Higher Regional Court"). On August 5, 2019 and October 31, 2019, the Higher Regional Court denied the Company and Sanofi's requests for a stay of preliminary enforcement of the July 11 Decision pending the appeal on the merits. On November 3, 2020, Amgen filed a motion withdrawing this lawsuit without prejudice. An oral hearing on the merits of the appeal to the Higher Regional Court was held on November 5, 2020, at which the Higher Regional Court overturned the July 11 Decision. France. On September 26, 2016, Amgen filed a lawsuit for infringement of the '124 Patent in the Tribunal de grande instance in Paris, France against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi Winthrop Industrie S.A., and Sanofi Chimie (subsequently added as a defendant). Amgen is seeking the prohibition of allegedly infringing activities with a €10,000 penalty per drug unit of Praluent produced in violation of the court order sought by Amgen; an appointment of an expert for the assessment of damages; disclosure of technical (including supply-chain) and accounting information to the expert and the court; provisional damages of €10.0 million (which would be awarded on an interim basis pending final determination); reimbursement of costs; publication of the ruling in three newspapers; and provisional enforcement of the decision to be issued, which would ensure enforcement of the decision (including any provisional damages) pending appeal. Amgen is not seeking a preliminary injunction in this proceeding at this time. On April 10, 2017, the Company and the Sanofi parties filed briefs seeking invalidation of certain of the claims of the '124 Patent, and Amgen filed a response on July 28, 2017. Oral hearing on this infringement lawsuit (originally scheduled for February 12, 2019) has yet to be rescheduled. The Netherlands. On December 17, 2019, Amgen initiated a lawsuit alleging infringement of the Dutch designation of the '124 Patent in the District Court of The Hague in the Netherlands, against Sanofi-Aventis Netherlands B.V. and Sanofi-Aventis Groupe S.A. The Company has not been named as a defendant in this action. Amgen alleges, among other things, patent infringement based on the production, importation, and commercialization of Praluent (alirocumab) in the Netherlands. Amgen's requests are made on an accelerated basis and include, among other things, a request for a permanent injunction, damages, an order for customer information, a recall order, a destruction order, and an order for costs. A hearing has been scheduled for February 12, 2021. Italy. On December 20, 2019, Amgen filed a lawsuit for infringement of the Italian designation of the '124 Patent in the Tribunale di Milano - Enterprise Chamber in Milan, Italy, against Sanofi-Aventis Groupe S.A., Sanofi Chimie, and Sanofi SpA. The Company has not been named as a defendant in this action. Amgen alleges that the production, importation, and commercialization of Praluent (alirocumab) in Italy infringes the '124 Patent. The writ of summons filed by Amgen seeks, among other things, a declaration of infringement, a permanent injunction, withdrawal of product from the market, and damages. On June 24, 2020, Amgen also filed a preliminary injunction motion against the Sanofi parties. On August 12, 2020, the court denied Amgen's preliminary injunction motion. Spain. On December 20, 2019, Amgen also filed a lawsuit alleging infringement of the Spanish designation of the '124 Patent in the Juzgado de lo Mercantil No. 5 (Commercial Court) in Barcelona, Spain, against Sanofi-Aventis, S.A. The Company was not named as a defendant in this action. Amgen alleged, among other things, patent infringement based on the manufacture, offering for sale, introduction into the market, use, and importation or possession of Praluent (alirocumab) in Spain. Amgen sought, among other things, a permanent injunction, withdrawal of Praluent from the market, seizure and destruction of Praluent from the market and in storage, and damages in the form of lost profits and costs and expenses. On May 12, 2020, the court stayed this lawsuit until October 30, 2020 on terms mutually agreed by the parties. On October 30, 2020, the stay was automatically lifted. On November 2, 2020, Amgen filed a motion withdrawing this lawsuit; and, on February 1, 2021, the lawsuit was dismissed. Other Japan. On May 19, 2017, Amgen filed a lawsuit for infringement of Amgen's Japanese Patent Nos. 5,906,333 (the "'333 Patent") and 5,705,288 (the "'288 Patent") in the Tokyo District Court Civil Division (the "Tokyo District Court") against Sanofi K.K. Amgen's complaint alleges that manufacturing, selling or otherwise transferring, and offering to sell or otherwise transfer Praluent (alirocumab) in Japan (as well as importing Praluent (alirocumab) into Japan) infringe the '333 and '288 Patents. The complaint further seeks a permanent injunction, disposal of product, and court costs. The Company has not been named as a defendant in this litigation. On January 17, 2019, the Tokyo District Court upheld the validity of the '333 Patent and '288 Patent and ordered a permanent injunction against Sanofi K.K. to stop manufacturing, selling or otherwise transferring, and offering to sell or otherwise transfer Praluent (alirocumab) in Japan (as well as importing Praluent (alirocumab) into Japan) and to dispose of all product. However, the Tokyo District Court stayed the enforcement of such injunction pending appeal to the Intellectual Property High Court of Japan (the "IPHC"). On January 30, 2019, Sanofi K.K. appealed the Tokyo District Court's decision in the infringement proceedings to the IPHC. Following an oral hearing on October 30, 2019, the IPHC affirmed the Tokyo District Court's decision in the infringement proceedings. Sanofi K.K. appealed the IPHC's decision in the infringement proceedings to the Supreme Court of Japan on November 12, 2019. On April 24, 2020, the Supreme Court of Japan declined to hear the appeal filed by Sanofi K.K. in the infringement proceedings and the injunction issued by the Tokyo District Court became effective. Sanofi K.K. subsequently complied with the injunction and, as a result, the commercialization of Praluent in Japan has been discontinued. On March 31, 2020, Amgen filed a related lawsuit in the Tokyo District Court against Sanofi K.K. seeking damages incurred by Amgen as a result of the finding of infringement of the '333 Patent and the '288 Patent. The Company has not been named as a defendant in this damages action. Proceedings Relating to Dupixent (dupilumab) Injection United States On March 20, 2017, the Company, Sanofi-Aventis U.S. LLC, and Genzyme Corporation filed a lawsuit against Amgen and Immunex Corporation, a wholly owned subsidiary of Amgen, in the United States District Court for the District of Massachusetts seeking a declaratory judgment that the Company's and the other plaintiffs' Commercializing of Dupixent does not directly or indirectly infringe U.S. Patent No. 8,679,487 (the "'487 Patent") owned by Immunex Corporation relating to antibodies that bind the human interleukin-4 receptor. On May 1, 2017, the Company and the other plaintiffs filed a notice of voluntary dismissal of this action without prejudice. On March 23, 2017, the Company, Sanofi-Aventis U.S. LLC, and Genzyme Corporation initiated an inter partes review ("IPR") in the United States Patent and Trademark Office ("USPTO") seeking a declaration of invalidity of the '487 Patent. On July 28 and 31, 2017, the same parties filed two additional IPR petitions in the USPTO seeking declarations of invalidity of the '487 Patent based on different grounds (the "Additional IPR Petitions"). On October 4, 2017, the Patent Trial and Appeal Board ("PTAB") of the USPTO issued a decision on the first IPR petition and declined to institute an IPR proceeding to review the validity of the '487 Patent. On February 15, 2018, the PTAB issued two decisions instituting the Company's and Sanofi's Additional IPR Petitions on all claims of the '487 Patent for which review had been requested. Oral hearings on the Additional IPR Petitions before the PTAB were held on November 14, 2018. On February 14, 2019, the PTAB issued final written decisions on the Additional IPR Petitions, invalidating all 17 claims of the '487 Patent as obvious based on one of the Additional IPR Petitions while declining to hold the challenged claims of the '487 Patent invalid based on the other. In April 2019, the parties filed notices of appeal with the Federal Circuit appealing the PTAB's respective adverse final written decisions on the Additional IPR Petitions, and oral argument was held on August 5, 2020. On October 13, 2020, the Federal Circuit affirmed the PTAB's decision on the Additional IPR Petition that invalidated all 17 claims of the '487 Patent as obvious. On April 5, 2017, Immunex Corporation filed a lawsuit against the Company, Sanofi, Sanofi-Aventis U.S. LLC, Genzyme Corporation, and Aventisub LLC in the United States District Court for the Central District of California seeking a judgment of patent infringement of the '487 Patent and a declaratory judgment of infringement of the '487 Patent, in each case by the Company's and the other defendants' Commercializing of Dupixent; monetary damages (together with interest); an order of willful infringement of the '487 Patent, which would allow the court in its discretion to award damages up to three times the amount assessed; costs and expenses of the lawsuit; and attorneys' fees. Immunex is not seeking an injunction in this proceeding at this time. On June 21, 2017, the court denied a motion to dismiss Immunex's complaint previously filed by the Company and the Sanofi parties. On June 28, 2017, the Company and the Sanofi parties filed an answer to Immunex's complaint and counterclaims against Immunex and Amgen (which was amended on October 31, 2017 to, among other things, add an inequitable conduct allegation), and Immunex and Amgen filed an answer to the counterclaims on July 28, 2017. A combined hearing on the construction of certain disputed claim terms of the '487 Patent and the Company and the Sanofi parties' motion for summary judgment on the issue of indefiniteness of the '487 Patent claims was held on July 12, 2018. On August 24, 2018, the court issued an order denying this motion and construed the disputed claim terms as proposed by Amgen. On February 28, 2019, the court granted a joint stipulation by the parties to stay the litigation pending resolution of the appeals of the PTAB's final written decisions on the Additional IPR Petitions discussed above. Europe On September 30, 2016, Sanofi initiated a revocation proceeding in the United Kingdom to invalidate the U.K. counterpart of European Patent No. 2,292,665 (the "'665 Patent"), another patent owned by Immunex relating to antibodies that bind the human interleukin-4 receptor. At the joint request of the parties to the revocation proceeding, the U.K. Patents Court ordered on January 30, 2017 that the revocation action be stayed pending the final determination of the currently pending EPO opposition proceedings initiated by the Company and Sanofi in relation to the '665 Patent. The oral hearing before the EPO on the oppositions occurred on November 20, 2017, at which the claims of the '665 Patent were found invalid and the patent was revoked. A final written decision of revocation of the '665 Patent was issued by the EPO on January 4, 2018. Immunex filed a notice of appeal of the EPO's decision on January 31, 2018. On September 20, 2017 and September 21, 2017, respectively, the Company and Sanofi initiated opposition proceedings in the EPO against Immunex's European Patent No. 2,990,420 (the "'420 Patent"), a divisional patent of the '665 Patent (i.e., a patent that shares the same priority date, disclosure, and patent term of the parent '665 Patent but contains claims to a different invention). The oral hearing before the EPO on the oppositions occurred on February 14–15, 2019, at which the '420 Patent was revoked in its entirety. Immunex filed a notice of appeal of the EPO's decision on May 31, 2019. The original patent term of the Immunex patents is set to expire in 2021. Proceedings Relating to EYLEA (aflibercept) Injection On January 7, 2021, Chengdu Kanghong Pharmaceutical Group Co., Ltd. filed an IPR petition in the USPTO against the Company' s U.S. Patent No. 10,464,992 (the "'992 Patent") and a post-grant review petition against the Company's U.S. Patent No. 10,828,345 (the "'345 Patent") seeking declarations of invalidity of the '992 Patent and '345 Patent. Proceedings Relating to EYLEA (aflibercept) Injection Pre-filled Syringe On June 19, 2020, Novartis Pharma AG, Novartis Pharmaceuticals Corporation, and Novartis Technology LLC (collectively, "Novartis") filed a complaint with the U.S. International Trade Commission (the "ITC") pursuant to Section 337 of the Tariff Act of 1930 requesting that the ITC institute an investigation relating to the importation into the United States and/or sale within the United States after importation of EYLEA pre-filled syringes ("PFS") and/or components thereof which allegedly infringe Novartis’s U.S. Patent No. 9,220,631 (the "'631 Patent"). Novartis also requested a permanent limited exclusion order forbidding entry into the United States of EYLEA PFS or components thereof; a permanent cease-and-desist order from the importation, sale, offer for sale, advertising, packaging, or solicitation of any sale by the Company of EYLEA PFS or components thereof; and a bond should the Company continue to import EYLEA PFS (if found to infringe) during, if applicable, any 60-day Presidential review period (i.e., the period when the President of the United States (or his designee) can disapprove any ITC decision to issue an exclusion order or cease-and-desist order). The ITC instituted the investigation on July 22, 2020 and a trial has been scheduled for April 19-23, 2021. On June 19, 2020, Novartis also filed a patent infringement lawsuit in the U.S. District Court for the Northern District of New York asserting claims of the '631 Patent and seeking preliminary and permanent injunctions to prevent the Company from continuing to infringe the '631 Patent. Novartis also seeks a judgment of patent infringement of the '631 Patent, monetary damages (together with interest), treble damages, costs and expenses of the lawsuits, and attorneys' fees. On July 30, 2020, the court granted the Company's motion to stay these proceedings until a determination in the ITC proceedings discussed above, including any appeals therefrom, becomes final. On July 16, 2020, the Company initiated two IPR petitions in the USPTO seeking a declaration of invalidity of the '631 Patent on two separate grounds. On January 15, 2021, the USPTO declined to institute an IPR proceeding on procedural grounds in light of the pending ITC investigation discussed above; the other IPR petition has been withdrawn. On July 17, 2020, the Company filed an antitrust lawsuit against Novartis and Vetter Pharma International Gmbh ("Vetter") in the United States District Court for the Southern District of New York seeking a declaration that the '631 Patent is unenforceable and a judgment that the defendants' conduct violates Sections 1 and 2 of the Sherman Antitrust Act of 1890, as amended (the "Sherman Antitrust Act"). The Company is also seeking injunctive relief and treble damages. On September 4, 2020, Novartis filed, and Vetter moved to join, a motion to dismiss the complaint, to transfer the lawsuit to the Northern District of New York, or to stay the suit; and on October 19, 2020, Novartis filed, and Vetter moved to join, a second motion to dismiss the complaint on different grounds. On January 25, 2021, the Company filed an amended complaint seeking a judgment that the Novartis's conduct violates Section 2 of the Sherman Antitrust Act based on additional grounds, as well as a judgment of tortious interference with contract. Proceedings Related to "Most Favored Nation" Interim Final Rule On December 11, 2020, the Company filed a lawsuit in the United States District Court for the Southern District of New York against the U.S. Department of Health and Human Services, the Secretary of HHS, the Centers for Medicare & Medicaid Services ("CMS"), and the Administrator of CMS seeking declaratory and injunctive relief related to the interim final rule with comment period entitled "Most Favored Nation (MFN) Model" issued on November 20, 2020 by HHS, acting through CMS. On the same day, the Company filed a motion for a preliminary injunction and temporary restraining order, seeking to prevent implementation of the MFN Rule. On December 22, 2020, the court heard oral argument on the Company's motion for a preliminary injunction and temporary restraining order. On December 31, 2020, the court granted the Company's motion and issued a preliminary injunction. On February 2, 2021, the government stated to the court that the Solicitor General had determined not to appeal the preliminary injunction. Proceedings Relating to fasinumab On May 21, 2020, the Company and Teva Pharmaceutical Industries Limited ("Teva") filed a lawsuit against Rinat Neurosciences Corp. ("Rinat"), a wholly owned subsidiary of Pfizer Inc., in the English High Court of Justice in London, seeking invalidation and revocation of Rinat's European Patent No. 2,270,048 (the "'048 Patent"), European Patent No. 1,871,416 (the "'416 Patent"), and European Patent No. 2,305,711 (the "'711 Patent"), each of which pertains to the use of NGF monoclonal antibodies to treat certain symptoms in patients suffering from osteoarthritis. On July 21, 2020, Rinat filed its defense and counterclaim seeking a declaration of infringement of the '048 Patent by fasinumab. The counterclaim also seeks a permanent injunction, damages, an accounting of profits, and costs and interest. On December 15, 2020, Rinat filed an amended defense and counterclaim seeking a declaration of infringement of the '711 Patent by fasinumab. A trial has been scheduled to commence in late November or early December 2021. The '048 Patent is subject to opposition proceedings in the EPO, which were initiated by the Company on August 10, 2016 and two other opponents on August 11, 2016. On January 3, 2018, the Opposition Division of the EPO issued a preliminary, non-binding opinion regarding the validity of the '048 Patent, indicating that it considered the granted patent to be invalid. An oral hearing on the oppositions against the '048 Patent was held on November 29–30, 2018, at which the Opposition Division upheld the validity of the '048 Patent's claims in amended form. The Company filed a notice of appeal to the TBA of the EPO on March 7, 2019. On October 21, 2020, Teva filed a notice of intervention with the TBA to take part in the appeal proceedings as an intervener. The '711 Patent is also subject to opposition proceedings in the EPO, which were initiated by the Company on May 1, 2018. On January 31, 2019, the Opposition Division of the EPO issued a preliminary, non-binding opinion regarding the validity of the '711 Patent, indicating that it considered the granted patent to be invalid. An oral hearing on the opposition against the '711 Patent was held on December 3, 2019, at which the Opposition Division upheld the validity of the '711 Patent's claims in amended form. The Company filed a notice of appeal to the TBA on December 20, 2019. An oral hearing before the TBA has been scheduled for July 29, 2021. On January 29, 2021, Teva filed a notice of intervention with the TBA to take part in the appeal proceedings as an intervener. Proceedings Relating to REGEN-COV (casirivimab and imdevimab) On October 5, 2020, Allele Biotechnology and Pharmaceuticals, Inc. ("Allele") filed a lawsuit against the Company in the United States District Court for the Southern District of New York, asserting infringement of U.S. Patent No. 10,221,221 (the "'221 Patent"). Allele seeks a judgment of patent infringement of the '221 Patent, a judgment that such infringement was willful, and an award of monetary damages (together with interest), treble damages, costs and expenses of the lawsuit, and attorneys' fees. Department of Justice Matters In January 2017, the Company received a subpoena from the U.S. Attorney's Office for the District of Massachusetts requesting documents relating to its support of 501(c)(3) organizations that provide financial assistance to patients; documents concerning its provision of financial assistance to patients with respect to products sold or developed by Regeneron (including EYLEA, Praluent, ARCALYST, and ZALTRAP); and certain other related documents and communications. On June 24, 2020, the U.S. Attorney's Office for the District of Massachusetts filed a civil complaint in the U.S. District Court for the District of Massachusetts alleging violations of the federal Anti-Kickback Statute, and asserting causes of action under the federal False Claims Act and state law. On August 24, 2020, the Company filed a motion to dismiss the complaint in its entirety. On December 4, 2020, the court denied the motion to dismiss. In September 2019, the Company and Regeneron Healthcare Solutions, Inc., a wholly-owned subsidiary of the Company, each received a civil investigative demand ("CID") from the U.S. Department of Justice pursuant to the federal False Claims Act relating to remuneration paid to physicians in the form of consulting fees, advisory boards, speaker fees, and payment or reimbursement for travel and entertainment allegedly in violation of the federal Anti-Kickback Statute. The CIDs relate to EYLEA, Praluent, Dupixent, ZALTRAP, ARCALYST, and Kevzara and cover the period from January 2015 to the present. The Company is cooperating with this investigation. Proceedings Initiated by UnitedHealthcare On December 17, 2020, UnitedHealthcare Insurance Company and United Healthcare Services, Inc. (collectively, "UHC") filed a lawsuit against the Company in the United States District Court for the Southern District of New York alleging UHC has been damaged by the conduct alleged in the civil complaint filed by the U.S. Attorney's Office for the District of Massachusetts discussed under "Department of Justice Matters" above. UHC alleges causes of action under state law and the federal Racketeer Influenced and Corrupt Organizations Act and seeks monetary damages and equitable relief. Shareholder Demand On or about September 30, 2020, the Company's board of directors received a demand letter from a purported shareholder of the Company. The demand alleges that Regeneron and its shareholders have been damaged by the conduct alleged in the civil complaint filed by the U.S. Attorney's Office for the District of Massachusetts discussed under "Department of Justice Matters" above. The demand letter requests that the Company's board of directors investigate alleged breaches of fiduciary duty by its officers and directors and other alleged violations of law and corporate governance practices and procedures; bring legal action against the persons responsible for causing the alleged damages; and implement and maintain an effective system of internal controls, compliance mechanisms, and corporate governance practices and procedures. The Company's board of directors, working with outside counsel, investigated and evaluated the allegations in the demand letter and has concluded that pursuing the claims alleged in the demand would not be in the Company's best interests at this time.

Net Income Per Share

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Income Per Share

The calculations of basic and diluted net income per share are as follows:


	Year Ended December 31,
	2020		2019		2018
Net income - basic and diluted	$	3,513.2	$	2,115.8	$	2,444.4

(Shares in millions)
Weighted average shares - basic	107.6		109.2		107.9
Effect of dilutive securities:
Stock options	7.0		5.4		6.9
Restricted stock	0.5		—		—
Weighted average shares - diluted	115.1		114.6		114.8

Net income per share - basic	$	32.65	$	19.38	$	22.65
Net income per share - diluted	$	30.52	$	18.46	$	21.29

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive, include the following:


	Year Ended December 31,
(Shares in millions)	2020	2019	2018
Stock options	2.7	18.4	14.9

Statement of Cash Flows

12 Months Ended

Dec. 31, 2020

Cash and Cash Equivalents [Abstract]

Statement of Cash Flows

The following provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Consolidated Balance Sheet to the total of the same such amounts shown in the Consolidated Statement of Cash Flows:


	December 31,
	2020		2019		2018
Cash and cash equivalents	$	2,193.7	$	1,617.8	$	1,467.7
Restricted cash included in Other noncurrent assets	13.6		12.5		12.5
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statement of Cash Flows	$	2,207.3	$	1,630.3	$	1,480.2

Restricted cash consists of amounts held by financial institutions pursuant to contractual arrangements.

Supplemental disclosure of non-cash investing and financing activities

Included in accounts payable, accrued expenses, and other liabilities as of December 31, 2020, 2019, and 2018 were $83.6 million, $133.7 million, and $54.5 million, respectively, of accrued capital expenditures.

As described in Note 11, during 2020, 2019, and 2018, we purchased (by issuing a credit towards the amount owed by Sanofi) shares of our Common Stock from Sanofi to satisfy Sanofi's funding obligation related to Libtayo development costs.

Unaudited Quarterly Results

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Unaudited Quarterly Results

Summarized quarterly financial data (unaudited) for the years ended December 31, 2020 and 2019 are set forth in the following tables. Certain revisions have been made to the previously reported 2019 quarterly amounts below in connection with changing the presentation of certain amounts earned from collaborators (see Note 1 for further details).


	First Quarter Ended March 31, 2020		Second Quarter Ended June 30, 2020(1)		Third Quarter Ended September 30, 2020		Fourth Quarter Ended December 31, 2020(2)
Revenues	$	1,828.2	$	1,952.0	$	2,294.0	$	2,422.9
Operating expenses	$	1,128.1	$	1,295.6	$	1,240.9	$	1,255.9
Net income	$	624.6	$	897.3	$	842.1	$	1,149.2
Net income per share - basic	$	5.69	$	8.19	$	7.98	$	10.90
Net income per share - diluted	$	5.43	$	7.61	$	7.39	$	10.24


	First Quarter Ended March 31, 2019		Second Quarter Ended June 30, 2019(3)		Third Quarter Ended September 30, 2019		Fourth Quarter Ended December 31, 2019
Revenues	$	1,372.6	$	1,577.8	$	1,743.7	$	1,863.5
Operating expenses	$	892.6	$	1,262.2	$	1,005.2	$	1,187.8
Net income	$	461.1	$	193.1	$	669.6	$	792.0
Net income per share - basic	$	4.23	$	1.77	$	6.12	$	7.25
Net income per share - diluted	$	3.99	$	1.68	$	5.86	$	6.93

(1) Included in operating expenses (specifically, research and development expenses) were $85.0 million in up-front payments in connection with our collaboration agreement with Intellia. See Note 3.
(2) Included in operating expenses was (i) the recognition of cumulative catch-up adjustments of $99.8 million, net, in other operating income related to updates to estimates of the total research and development costs expected to be incurred for certain collaboration agreements (see Note 3), as well as (ii) a reversal of $95.0 million within selling, general, and administrative expenses for litigation-related loss contingency accruals in connection with proceedings for Praluent outside the United States (see Note 15).
(3) Included in operating expenses (specifically, research and development expenses) was a $400.0 million up-front payment in connection with our collaboration agreement with Alnylam. See Note 3.

Business Overview and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

financial statements as of and for the year ended December 31, 2020; however, actual results could differ from those estimates and there may be changes to our estimates in future periods.

Concentration of Credit Risk

Cash and Cash Equivalents

Debt and Equity Securities

Accounts Receivable

Accounts ReceivableThe Company's trade accounts receivable arise from product sales and represent amounts due from its customers, which are all located in the United States. In addition, the Company records accounts receivable arising from its collaboration and licensing agreements. The Company monitors the financial performance and credit worthiness of its counterparties so that it can properly assess and respond to changes in their credit profile. The Company provides allowances against receivables for estimated losses, if any, that may result from a counterparty's inability to pay. Amounts determined to be uncollectible are written-off against the allowance.

Inventories

Inventories are stated at the lower of cost or net realizable value. The Company determines the cost of inventory using the first-in, first-out, or FIFO, method.

Property, Plant and Equipment

Property, Plant, and Equipment


Building and improvements						10–50 years
Laboratory and other equipment						3–10 years
Furniture and fixtures						5 years

Leases

Operating leases

Finance leases

Revenue Recognition

Revenue Recognition - Product Revenue

Revenue from product sales is recognized at a point in time when our customer is deemed to have obtained control of the product, which generally occurs upon receipt by our customer.

Collaborative Arrangements


Nature/Type of Payment						Statement of Operations Presentation
Regeneron's share of profits or losses in connection with commercialization of products						Collaboration revenue
Reimbursement for manufacturing of commercial supplies						Collaboration revenue
Royalties and/or sales-based milestones earned						Collaboration revenue
Reimbursement of Regeneron's research and development expenses						Reduction to Research and development expenses
Regeneron's obligation for its share of collaborator's research and development expenses						Research and development expense
Up-front and development milestone payments to collaborators						Research and development expense
Reimbursement of Regeneron's commercialization-related expenses						Reduction to Selling, general, and administrative expense
Regeneron's obligation for its share of collaborator's commercialization-related expenses						Selling, general, and administrative expense
Regeneron's obligation to pay collaborator for its share of gross profits when Regeneron is deemed to be the principal						Cost of goods sold
Up-front and development milestones earned (when we have a combined unit of account which includes a license and providing research and development services)						Other operating income

•receive royalties and/or sales-based milestone payments from our collaborator, we recognize such amounts in the period earned.

Research and Development Expenses

Stock-based Compensation

Income Taxes

Per Share Data

Per Share DataBasic net income per share is computed by dividing net income by the weighted average number of shares of Common Stock and Class A Stock outstanding. Net income per share is presented on a combined basis, inclusive of Common Stock and Class A Stock outstanding, as each class of stock has equivalent economic rights. Basic net income per share excludes restricted stock until vested. Diluted net income per share includes the potential dilutive effect of common stock equivalents as if such securities were converted or exercised during the period, when the effect is dilutive. Common stock equivalents include: (i) outstanding stock options and unvested restricted stock under the Company's long-term incentive plans, which are included under the treasury stock method when dilutive, and (ii) Common Stock that would be issued upon the achievement of certain market conditions, which are included under the treasury stock method when dilutive.

Recently Issued Accounting Standards

Recently Adopted Accounting Standards

Legal Matters

Costs associated with the Company's involvement in legal proceedings are expensed as incurred.

Business Overview and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of reclassifications

The tables below present the impact of the change on the Company’s previously-filed Consolidated Balance Sheet as of December 31, 2019, the Consolidated Statement of Operations for the years ended December 31, 2019, and 2018, and the Consolidated Statement of Cash Flows for the years ended December 31, 2019, and 2018. The Company’s previously-filed balance sheet has been updated to reflect the addition of the caption Other liabilities for the presentation of up-front and development milestones paid by collaborators that are deferred. There was no impact on the Company’s previously-filed Consolidated Statements of Stockholders’ Equity.


	December 31, 2019
Balance Sheet Data:	As Previously Reported		Adjustments		As Revised
Accrued expenses and other current liabilities	$	1,086.8	$	124.6	$	1,211.4
Deferred revenue - Sanofi (current)	$	395.5	$	(85.0)	$	310.5
Deferred revenue - other (current)	$	196.2	$	(124.6)	$	71.6
Other liabilities - Sanofi (current)	—		$	85.0	$	85.0
Deferred revenue - Sanofi (noncurrent)	$	509.7	$	(482.0)	$	27.7
Deferred revenue - other (noncurrent)	$	109.3	$	(31.7)	$	77.6
Other liabilities - Sanofi (noncurrent)	—		$	482.0	$	482.0
Other noncurrent liabilities	$	286.0	$	31.7	$	317.7


	Year Ended December 31, 2019						Year Ended December 31, 2018
Statement of Operations Data:	As Previously Reported		Adjustments		As Revised		As Previously Reported		Adjustments		As Revised
Sanofi collaboration revenue	$	1,426.8	$	(1,023.2)	$	403.6	$	1,111.1	$	(1,236.8)	$	(125.7)
Bayer collaboration revenue	$	1,188.8	$	(43.2)	$	1,145.6	$	1,076.7	$	(40.6)	$	1,036.1
Other revenue	$	413.4	$	(239.4)	$	174.0	$	416.8	$	(287.8)	$	129.0
Total revenues	$	7,863.4	$	(1,305.8)	$	6,557.6	$	6,710.8	$	(1,565.2)	$	5,145.6

Research and development	$	3,036.6	$	(586.6)	$	2,450.0	$	2,186.1	$	(717.3)	$	1,468.8
Selling, general, and administrative	$	1,834.8	$	(492.9)	$	1,341.9	$	1,556.2	$	(429.0)	$	1,127.2
Cost of collaboration and contract manufacturing(1)	$	419.9	$	(17.1)	$	402.8	$	254.1	$	(16.6)	$	237.5
Other operating (income) expense, net	—		$	(209.2)	$	(209.2)	—		$	(402.3)	$	(402.3)
Total operating expenses	$	5,653.6	$	(1,305.8)	$	4,347.8	$	4,176.4	$	(1,565.2)	$	2,611.2

(1) In addition to the reclassification of certain amounts in connection with the change in accounting presentation described above, the Company also reclassified certain immaterial reimbursements that were previously classified as collaboration revenue to Cost of collaboration and contract manufacturing.


	Year Ended December 31, 2019						Year Ended December 31, 2018
Cash Flows Data:	As Previously Reported		Adjustments		As Revised		As Previously Reported		Adjustments		As Revised
Cash flows from operating activities:
Increase (decrease) in deferred revenue	$	294.0	$	(154.5)	$	139.5	$	(194.5)	$	151.1	$	(43.4)
Increase in accounts payable, accrued expenses, and other liabilities	$	444.5	$	154.5	$	599.0	$	209.9	$	(151.1)	$	58.8

Schedule of estimated useful lives of property, plant, and equipment

The estimated useful lives of property, plant, and equipment are as follows:


Building and improvements						10–50 years
Laboratory and other equipment						3–10 years
Furniture and fixtures						5 years

Property, plant, and equipment consists of the following:


	As of December 31,
	2020		2019
Land	$	241.2	$	230.8
Building and improvements	1,891.1		1,683.4
Leasehold improvements	100.5		97.6
Construction in progress	724.5		644.8
Laboratory equipment	1,038.6		850.7
Computer equipment and software	226.3		183.7
Furniture, office equipment, and other	130.5		121.8
	4,352.7		3,812.8
Less, accumulated depreciation and amortization	(1,131.1)		(922.4)
	$	3,221.6	$	2,890.4

Summary of presentation in statement of operations of payments to and from collaborators


Nature/Type of Payment						Statement of Operations Presentation
Regeneron's share of profits or losses in connection with commercialization of products						Collaboration revenue
Reimbursement for manufacturing of commercial supplies						Collaboration revenue
Royalties and/or sales-based milestones earned						Collaboration revenue
Reimbursement of Regeneron's research and development expenses						Reduction to Research and development expenses
Regeneron's obligation for its share of collaborator's research and development expenses						Research and development expense
Up-front and development milestone payments to collaborators						Research and development expense
Reimbursement of Regeneron's commercialization-related expenses						Reduction to Selling, general, and administrative expense
Regeneron's obligation for its share of collaborator's commercialization-related expenses						Selling, general, and administrative expense
Regeneron's obligation to pay collaborator for its share of gross profits when Regeneron is deemed to be the principal						Cost of goods sold
Up-front and development milestones earned (when we have a combined unit of account which includes a license and providing research and development services)						Other operating income

Product Sales (Tables)

12 Months Ended

Dec. 31, 2020

Revenues [Abstract]

Schedule of product sales

Net product sales consist of the following:


	Year Ended December 31,
Net Product Sales in the United States	2020		2019		2018
EYLEA	$	4,947.2	$	4,644.2	$	4,076.7
Libtayo	270.7		175.7		14.8
Praluent	150.9		*		*
REGEN-COV	185.7		—		—
ARCALYST	13.1		14.5		14.7
	$	5,567.6	$	4,834.4	$	4,106.2

* Effective April 1, 2020, the Company is solely responsible for the development and commercialization of Praluent in the United States and records net product sales of Praluent in the United States. See Note 3 for further details.

Amounts recognized in our Statements of Operations in connection with our collaborations with Sanofi are detailed below:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Antibody:
Regeneron's share of profits (losses) in connection with commercialization of antibodies	Sanofi collaboration revenue	$	785.2	$	209.3	$	(227.0)
Sales-based milestone earned	Sanofi collaboration revenue	$	50.0	—		—
Reimbursement for manufacturing of commercial supplies	Sanofi collaboration revenue	$	368.0	$	216.0	$	113.7
Reimbursement of research and development expenses	Reduction of Research and development expense	$	226.7	$	277.7	$	265.3
Regeneron's obligation for its share of Sanofi research and development expenses	Research and development expense	$	(77.6)	$	(46.0)	$	(47.7)
Reimbursement of commercialization-related expenses	Reduction of Selling, general, and administrative expense	$	359.4	$	479.9	$	417.2
Regeneron's obligation for its share of Sanofi other expenses	Cost of collaboration and contract manufacturing	$	(21.5)	$	(12.8)	$	(16.1)

Immuno-oncology:
Regeneron's share of losses in connection with commercialization of Libtayo outside the United States	Sanofi collaboration revenue	$	(25.7)	$	(21.7)	$	(12.4)
Reimbursement for manufacturing of commercial supplies	Sanofi collaboration revenue	$	8.9	—		—
Reimbursement of research and development expenses	Reduction of Research and development expense	$	166.2	$	163.0	$	311.8
Reimbursement of commercialization-related expenses	Reduction of Selling, general, and administrative expense	$	64.7	$	10.3	$	8.9
Regeneron's obligation for Sanofi's share of Libtayo U.S. gross profits	Cost of goods sold	$	(119.1)	$	(78.2)	$	(6.8)
Amounts recognized in connection with up-front payments received	Other operating income	$	210.6	$	92.7	$	243.8

Amounts recognized in our Statements of Operations in connection with our Bayer EYLEA collaboration are as follows:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	Bayer collaboration revenue	$	1,107.9	$	1,091.4	$	992.3
Reimbursement for manufacturing of commercial supplies	Bayer collaboration revenue	$	78.2	$	54.2	$	43.8
Reimbursement of development expenses	Reduction of Research and development expense	$	46.7	$	23.0	$	11.2
Regeneron's obligation for its share of Bayer research and development expenses	Research and development expense	$	(35.8)	$	(20.1)	$	(0.5)
Reimbursement of other expenses	Cost of collaboration and contract manufacturing	$	7.4	$	19.0	$	28.9

Amounts recognized in our Statements of Operations in connection with the Teva Collaboration Agreement are as follows:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Reimbursement of research and development expenses	Reduction of Research and development expense	$	109.4	$	122.9	$	129.5
Amounts recognized in connection with up-front and development milestone payments received	Other operating income	$	47.2	$	82.2	$	113.2

Schedules of concentration of risk, by risk factor

Sales to each of these customers as a percentage of the Company's total gross product revenue are as follows:


	Year Ended December 31,
	2020		2019		2018
Besse Medical, a subsidiary of AmerisourceBergen Corporation	51	%	57	%	56	%
McKesson Corporation	32	%	33	%	36	%

Sales related deductions activity

The following table summarizes the provisions, and credits/payments, for sales-related deductions for the years ended December 31, 2020, 2019, and 2018.


	Rebates, Chargebacks, and Discounts		Distribution- Related Fees		Other Sales- Related Deductions		Total
Balance as of December 31, 2017	$	29.9	$	34.1	$	21.3	$	85.3
Provisions	223.4		211.0		44.5		478.9
Credits/payments	(212.2)		(203.1)		(57.5)		(472.8)
Balance as of December 31, 2018	41.1		42.0		8.3		91.4
Provisions	423.2		242.9		61.8		727.9
Credits/payments	(384.0)		(238.5)		(40.7)		(663.2)
Balance as of December 31, 2019	80.3		46.4		29.4		156.1
Provisions	762.9		279.9		94.1		1,136.9
Credits/payments	(641.0)		(249.1)		(78.7)		(968.8)
Balance as of December 31, 2020	$	202.2	$	77.2	$	44.8	$	324.2

Collaboration, License, and Other Agreements (Tables)

12 Months Ended

Dec. 31, 2020

Revenue from Contract with Customer [Abstract]

Schedule of collaboration revenue

Net product sales consist of the following:


	Year Ended December 31,
Net Product Sales in the United States	2020		2019		2018
EYLEA	$	4,947.2	$	4,644.2	$	4,076.7
Libtayo	270.7		175.7		14.8
Praluent	150.9		*		*
REGEN-COV	185.7		—		—
ARCALYST	13.1		14.5		14.7
	$	5,567.6	$	4,834.4	$	4,106.2

* Effective April 1, 2020, the Company is solely responsible for the development and commercialization of Praluent in the United States and records net product sales of Praluent in the United States. See Note 3 for further details.

Amounts recognized in our Statements of Operations in connection with our collaborations with Sanofi are detailed below:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Antibody:
Regeneron's share of profits (losses) in connection with commercialization of antibodies	Sanofi collaboration revenue	$	785.2	$	209.3	$	(227.0)
Sales-based milestone earned	Sanofi collaboration revenue	$	50.0	—		—
Reimbursement for manufacturing of commercial supplies	Sanofi collaboration revenue	$	368.0	$	216.0	$	113.7
Reimbursement of research and development expenses	Reduction of Research and development expense	$	226.7	$	277.7	$	265.3
Regeneron's obligation for its share of Sanofi research and development expenses	Research and development expense	$	(77.6)	$	(46.0)	$	(47.7)
Reimbursement of commercialization-related expenses	Reduction of Selling, general, and administrative expense	$	359.4	$	479.9	$	417.2
Regeneron's obligation for its share of Sanofi other expenses	Cost of collaboration and contract manufacturing	$	(21.5)	$	(12.8)	$	(16.1)

Immuno-oncology:
Regeneron's share of losses in connection with commercialization of Libtayo outside the United States	Sanofi collaboration revenue	$	(25.7)	$	(21.7)	$	(12.4)
Reimbursement for manufacturing of commercial supplies	Sanofi collaboration revenue	$	8.9	—		—
Reimbursement of research and development expenses	Reduction of Research and development expense	$	166.2	$	163.0	$	311.8
Reimbursement of commercialization-related expenses	Reduction of Selling, general, and administrative expense	$	64.7	$	10.3	$	8.9
Regeneron's obligation for Sanofi's share of Libtayo U.S. gross profits	Cost of goods sold	$	(119.1)	$	(78.2)	$	(6.8)
Amounts recognized in connection with up-front payments received	Other operating income	$	210.6	$	92.7	$	243.8

Amounts recognized in our Statements of Operations in connection with our Bayer EYLEA collaboration are as follows:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	Bayer collaboration revenue	$	1,107.9	$	1,091.4	$	992.3
Reimbursement for manufacturing of commercial supplies	Bayer collaboration revenue	$	78.2	$	54.2	$	43.8
Reimbursement of development expenses	Reduction of Research and development expense	$	46.7	$	23.0	$	11.2
Regeneron's obligation for its share of Bayer research and development expenses	Research and development expense	$	(35.8)	$	(20.1)	$	(0.5)
Reimbursement of other expenses	Cost of collaboration and contract manufacturing	$	7.4	$	19.0	$	28.9

Amounts recognized in our Statements of Operations in connection with the Teva Collaboration Agreement are as follows:


	Statement of Operations Classification	Year Ended December 31,
		2020		2019		2018
Reimbursement of research and development expenses	Reduction of Research and development expense	$	109.4	$	122.9	$	129.5
Amounts recognized in connection with up-front and development milestone payments received	Other operating income	$	47.2	$	82.2	$	113.2

Schedule of accounts receivable and deferred revenue information

The following table summarizes contract balances in connection with the Company's Antibody Collaboration with Sanofi:


	As of December 31,
	2020		2019
Accounts receivable	$	407.7	$	272.7
Deferred revenue	$	347.7	$	328.8

The following table summarizes contract balances in connection with the Company's IO Collaboration with Sanofi:


	As of December 31,
	2020		2019
Accounts receivable, net	$	(6.5)	$	(16.7)
Deferred revenue	$	10.7	$	9.4
Other liabilities	$	280.9	$	558.6

Other liabilities include up-front payments received from Sanofi for which recognition has been deferred.

The following table summarizes contract balances in connection with our Bayer EYLEA collaboration:


	As of December 31,
	2020		2019
Accounts receivable - other	$	336.2	$	311.6
Deferred revenue	$	99.7	$	123.0

The following table summarizes contract balances in connection with the Teva Collaboration Agreement:


	As of December 31,
	2020		2019
Accounts receivable - other	$	27.7	$	21.2
Other liabilities	$	66.8	$	114.4

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Available-for-sale debt securities

The following tables summarize the Company's investments in available-for-sale debt securities:


	Amortized		Unrealized				Fair
As of December 31, 2020	Cost Basis		Gains		Losses		Value
Corporate bonds	$	3,053.0	$	37.5	$	(0.2)	$	3,090.3
U.S. government and government agency obligations	127.6		1.3		—		128.9
Sovereign bonds	65.2		1.1		—		66.3
Commercial paper	276.0		0.1		—		276.1
Certificates of deposit	127.4		0.1		—		127.5
	$	3,649.2	$	40.1	$	(0.2)	$	3,689.1

As of December 31, 2019
Corporate bonds	$	3,960.5	$	27.8	$	(0.2)	$	3,988.1
U.S. government and government agency obligations	54.3		0.2		(0.1)		54.4
Sovereign bonds	26.9		0.4		—		27.3
Commercial paper	92.3		—		—		92.3
Certificates of deposit	72.3		0.1		—		72.4
	$	4,206.3	$	28.5	$	(0.3)	$	4,234.5

Marketable securities, based on contractual maturity dates

The fair values of available-for-sale debt security investments by contractual maturity consist of the following:


	As of December 31,
	2020		2019
Maturities within one year	$	1,393.3	$	1,596.5
Maturities after one year through five years	2,295.8		2,638.0
	$	3,689.1	$	4,234.5

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of assets measured at fair value on a recurring basis

•Level 1 - Quoted prices in active markets for identical assets

•Level 3 - Significant other unobservable inputs


			Fair Value Measurements at Reporting Date
As of December 31, 2020	Fair Value		Level 1		Level 2
Available-for-sale debt securities:
Corporate bonds	$	3,090.3	—		$	3,090.3
U.S. government and government agency obligations	128.9		—		128.9
Sovereign bonds	66.3		—		66.3
Commercial paper	276.1		—		276.1
Certificates of deposit	127.5		—		127.5
Equity securities (unrestricted)	48.3		$	48.3	—
Equity securities (restricted)	791.5		791.5		—
	$	4,528.9	$	839.8	$	3,689.1

As of December 31, 2019
Available-for-sale debt securities:
Corporate bonds	$	3,988.1	—		$	3,988.1
U.S. government and government agency obligations	54.4		—		54.4
Sovereign bonds	27.3		—		27.3
Commercial paper	92.3		—		92.3
Certificates of deposit	72.4		—		72.4
Equity securities (unrestricted)	61.6		$	61.6	—
Equity securities (restricted)	557.2		557.2		—
	$	4,853.3	$	618.8	$	4,234.5

Inventories (Tables)

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

Schedule of inventory

Inventories consist of the following:


	As of December 31,
	2020		2019
Raw materials	$	459.4	$	216.3
Work-in-process	904.6		727.7
Finished goods	121.7		70.6
Deferred costs	430.9		400.9
	$	1,916.6	$	1,415.5

Property, Plant, and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Schedule of property, plant and equipment

The estimated useful lives of property, plant, and equipment are as follows:


Building and improvements						10–50 years
Laboratory and other equipment						3–10 years
Furniture and fixtures						5 years

Property, plant, and equipment consists of the following:


	As of December 31,
	2020		2019
Land	$	241.2	$	230.8
Building and improvements	1,891.1		1,683.4
Leasehold improvements	100.5		97.6
Construction in progress	724.5		644.8
Laboratory equipment	1,038.6		850.7
Computer equipment and software	226.3		183.7
Furniture, office equipment, and other	130.5		121.8
	4,352.7		3,812.8
Less, accumulated depreciation and amortization	(1,131.1)		(922.4)
	$	3,221.6	$	2,890.4

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

Schedule of accrued expenses and other current liabilities

Accrued expenses and other current liabilities consist of the following:


	As of December 31,
	2020		2019
Accrued payroll and related costs	$	465.8	$	344.4
Accrued clinical expenses	283.0		142.7
Accrued sales-related charges, deductions, and royalties	423.9		249.0
Income taxes payable	19.5		49.4
Other accrued expenses and liabilities	329.6		425.9
	$	1,521.8	$	1,211.4

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Schedule of amounts recognized in the Condensed Consolidated Balance Sheet


		As of December 31,
	Classification	2020		2019
Finance lease right-of-use assets	Property, plant, and equipment, net(1)	$	645.7	$	660.1
Finance lease liabilities	Finance lease liabilities (noncurrent)	$	717.2	$	713.9

(1) Finance lease right-of-use assets are recorded net of accumulated amortization of $90.5 million and $76.1 million as of December 31, 2020 and 2019, respectively.

Schedule of lease cost and other information

Finance lease costs consist of the following:


	Year Ended December 31,
	2020		2019
Amortization of right-of-use assets	$	14.4	$	14.4
Interest on lease liabilities	15.7		27.6
	$	30.1	$	42.0

Other information related to our finance lease includes the following:


	As of December 31,
	2020	2019
Remaining lease term (in years)	1.17	2.17
Discount rate	1.66%	3.05%

Schedule of maturities of finance lease liabilities

The following is a maturity analysis of our finance lease liabilities:


	As of December 31, 2020
2021	$	12.1
2022	723.1
2023	—
2024	—
2025	—
Thereafter	—
Total undiscounted lease payments	735.2
Imputed interest	(15.1)
Debt financing costs	(2.9)
Total lease liabilities	$	717.2

Equity (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Class of treasury stock

The table below summarizes the shares of our Common Stock we repurchased under the program and the cost of the shares received, which were recorded as Treasury Stock.


	Year Ended December 31,
	2020		2019
Number of shares repurchased	1,605,582		722,596
Total cost of shares received	$	746.0	$	254.0

The table below summarizes the shares of our Common Stock Sanofi elected to sell, and we elected to purchase, to satisfy Sanofi's funding obligations and the cost of the shares received, which were recorded as Treasury Stock.


	As of December 31,
	2020		2019		2018
Libtayo:
Number of shares purchased (by issuing a credit towards the amount owed by Sanofi)	77,677		210,733		215,387
Total cost of shares received	$	41.7	$	73.3	$	75.8

Dupilumab/Itepekimab:
Number of shares purchased (in cash)	171,471		93,286		10,766
Total cost of shares received	$	93.3	$	29.4	$	4.4

Long-Term Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of transactions involving stock option awards

Transactions involving stock option awards during 2020 under the Company's Incentive Plans are summarized in the table below.


		Number of Shares	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Intrinsic Value
Outstanding as of December 31, 2019		28,609,277	$	337.24
2020:	Granted	2,850,590	$	492.60
	Forfeited	(562,629)	$	379.02
	Expired	(56,282)	$	473.77
	Exercised	(9,139,287)	$	281.90
Outstanding as of December 31, 2020		21,701,669	$	379.51	6.34	$	2,347.4

Vested and expected to vest as of December 31, 2020		20,764,534	$	377.23	6.22	$	2,294.1

Exercisable as of December 31, 2020		13,648,899	$	357.65	4.96	$	1,799.1

Schedule of weighted-average exercise prices and weighted-average grant-date fair values of options issued

The table below summarizes the weighted-average exercise prices and weighted-average grant-date fair values of options issued during the years ended December 31, 2020, 2019, and 2018.


	Number of Options Granted	Weighted-Average Exercise Price		Weighted-Average Fair Value
2020:
Exercise price equal to Market Price	2,850,590	$	492.60	$	126.50
2019:
Exercise price equal to Market Price	3,271,222	$	366.65	$	100.80
2018:
Exercise price equal to Market Price	4,665,320	$	378.51	$	114.39

Schedule of weighted-average values of assumptions used in computing fair value of option grants

The following table summarizes the weighted average values of the assumptions used in computing the fair value of option grants during 2020, 2019, and 2018.


	2020		2019		2018
Expected volatility	28	%	28	%	29	%
Expected lives from grant date	5.0 years		5.0 years		4.9 years
Expected dividend yield	0	%	0	%	0	%
Risk-free interest rate	0.47	%	1.74	%	2.69	%

The following table summarizes the weighted average values of the assumptions used in computing the fair value of PSUs during 2020 and 2019.


	2020	2019
Expected volatility	35%	33%
Expected dividend yield	0%	0%
Risk-free interest rate	0.36%	1.63%

Schedule of activity related to restricted stock awards


		Number of Shares/Units	Weighted-Average Grant Date Fair Value
Balance as of December 31, 2019		1,102,390	$	377.32
2020:	Granted	646,844	$	496.44
	Vested	(15,630)	$	526.62
	Forfeited/Cancelled	(46,061)	$	377.85
Balance as of December 31, 2020		1,687,543	$	421.58

Schedule of activity related to performance-based awards

A summary of the Company's activity related to PSUs during 2020 is summarized below.


		Number of Shares/Units	Weighted-Average Grant Date Fair Value
Balance as of December 31, 2019		59,396	$	198.10
2020:	Granted	1,240,540	$	209.59
	Vested	—	—
	Forfeited/Cancelled	—	—
Balance as of December 31, 2020		1,299,936	$	209.06

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of income before income tax

Components of income before income taxes consist of the following:


	Year Ended December 31,
	2020		2019		2018
United States	$	2,442.3	$	2,011.2	$	2,151.7
Foreign	1,368.1		417.9		401.8
	$	3,810.4	$	2,429.1	$	2,553.5

Schedule of components of income tax expense

Components of income tax expense consist of the following:


	Year Ended December 31,
	2020		2019		2018
Current:
Federal	$	199.0	$	444.6	$	223.7
State	1.2		1.9		4.8
Foreign	21.4		(2.6)		20.6
Total current tax expense	221.6		443.9		249.1
Deferred:
Federal	109.0		(132.0)		687.6
State	(2.0)		(1.7)		(1.9)
Foreign	(31.4)		3.1		(825.7)
Total deferred tax (benefit) expense	75.6		(130.6)		(140.0)
	$	297.2	$	313.3	$	109.1

Schedule of effective income tax rate reconciliation

A reconciliation of the U.S. statutory income tax rate to the Company's effective income tax rate is as follows:


	Year Ended December 31,
	2020		2019		2018
U.S. federal statutory tax rate	21.0	%	21.0	%	21.0	%
Stock-based compensation	(7.6)		(2.5)		(2.5)
Income tax credits	(2.8)		(4.6)		(2.6)
Taxation of non-U.S. operations	(1.8)		(1.0)		(1.9)
Sale of non-inventory related assets between foreign subsidiaries	(0.8)		—		(6.3)
Foreign-derived intangible income deduction	—		(1.6)		(1.0)
Non-deductible Branded Prescription Drug Fee	0.5		0.7		0.6
Impact of change in U.S. corporate tax rate (the Act)	—		—		(2.7)
Other permanent differences	(0.7)		0.9		(0.3)
Effective income tax rate	7.8	%	12.9	%	4.3	%

Schedule of deferred tax assets and liabilities

Significant components of the Company's deferred tax assets and liabilities are as follows:


	As of December 31,
	2020		2019
Deferred tax assets:
Deferred compensation	$	436.6	$	519.7
Fixed assets and intangible assets	140.5		192.0
Accrued expenses	139.8		75.9
Deferred revenue	44.6		22.0
Total deferred tax assets	761.5		809.6
Valuation allowance	—		(7.0)
Deferred tax assets, net of valuation allowance	761.5		802.6

Deferred tax liabilities:
Other	(42.8)		(11.2)
Net deferred tax assets	$	718.7	$	791.4

Schedule of unrecognized tax benefits


	2020		2019		2018
Balance as of January 1	$	210.8	$	189.5	$	146.2
Gross increases related to current year tax positions	76.6		37.9		51.4
Gross increases (decreases) related to prior year tax positions	7.2		(7.2)		5.6
Gross decreases due to settlements and lapse of statutes of limitations	(27.6)		(9.4)		(13.7)
Balance as of December 31	$	267.0	$	210.8	$	189.5

Net Income Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Basic and diluted net income (loss) per share

The calculations of basic and diluted net income per share are as follows:


	Year Ended December 31,
	2020		2019		2018
Net income - basic and diluted	$	3,513.2	$	2,115.8	$	2,444.4

(Shares in millions)
Weighted average shares - basic	107.6		109.2		107.9
Effect of dilutive securities:
Stock options	7.0		5.4		6.9
Restricted stock	0.5		—		—
Weighted average shares - diluted	115.1		114.6		114.8

Net income per share - basic	$	32.65	$	19.38	$	22.65
Net income per share - diluted	$	30.52	$	18.46	$	21.29

Antidilutive securities

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive, include the following:


	Year Ended December 31,
(Shares in millions)	2020	2019	2018
Stock options	2.7	18.4	14.9

Statement of Cash Flows (Tables)

12 Months Ended

Dec. 31, 2020

Cash and Cash Equivalents [Abstract]

Schedule of cash and cash equivalents


	December 31,
	2020		2019		2018
Cash and cash equivalents	$	2,193.7	$	1,617.8	$	1,467.7
Restricted cash included in Other noncurrent assets	13.6		12.5		12.5
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statement of Cash Flows	$	2,207.3	$	1,630.3	$	1,480.2

Schedule of restrictions on cash and cash equivalents


	December 31,
	2020		2019		2018
Cash and cash equivalents	$	2,193.7	$	1,617.8	$	1,467.7
Restricted cash included in Other noncurrent assets	13.6		12.5		12.5
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statement of Cash Flows	$	2,207.3	$	1,630.3	$	1,480.2

Unaudited Quarterly Results (Tables)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Schedule of quarterly financial information


	First Quarter Ended March 31, 2020		Second Quarter Ended June 30, 2020(1)		Third Quarter Ended September 30, 2020		Fourth Quarter Ended December 31, 2020(2)
Revenues	$	1,828.2	$	1,952.0	$	2,294.0	$	2,422.9
Operating expenses	$	1,128.1	$	1,295.6	$	1,240.9	$	1,255.9
Net income	$	624.6	$	897.3	$	842.1	$	1,149.2
Net income per share - basic	$	5.69	$	8.19	$	7.98	$	10.90
Net income per share - diluted	$	5.43	$	7.61	$	7.39	$	10.24


	First Quarter Ended March 31, 2019		Second Quarter Ended June 30, 2019(3)		Third Quarter Ended September 30, 2019		Fourth Quarter Ended December 31, 2019
Revenues	$	1,372.6	$	1,577.8	$	1,743.7	$	1,863.5
Operating expenses	$	892.6	$	1,262.2	$	1,005.2	$	1,187.8
Net income	$	461.1	$	193.1	$	669.6	$	792.0
Net income per share - basic	$	4.23	$	1.77	$	6.12	$	7.25
Net income per share - diluted	$	3.99	$	1.68	$	5.86	$	6.93

(1) Included in operating expenses (specifically, research and development expenses) were $85.0 million in up-front payments in connection with our collaboration agreement with Intellia. See Note 3.
(2) Included in operating expenses was (i) the recognition of cumulative catch-up adjustments of $99.8 million, net, in other operating income related to updates to estimates of the total research and development costs expected to be incurred for certain collaboration agreements (see Note 3), as well as (ii) a reversal of $95.0 million within selling, general, and administrative expenses for litigation-related loss contingency accruals in connection with proceedings for Praluent outside the United States (see Note 15).
(3) Included in operating expenses (specifically, research and development expenses) was a $400.0 million up-front payment in connection with our collaboration agreement with Alnylam. See Note 3.

Business Overview and Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of business segments \| segment	1
Retained Earnings (Accumulated Deficit)	$ 10,893,000,000.0	$ 7,379,800,000
Allowance for doubtful accounts receivable, current	0	0
Provision for doubtful accounts	0	0
Up-front and development milestone revenue recognized	$ 276,700,000	$ 207,200,000
Three individual customers \| Customer concentration risk \| Gross Sales Revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Concentration risk, percentage	93.00%	97.00%
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset			$ 33,200,000
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained Earnings (Accumulated Deficit)				$ (143,400,000)
Deferred revenue				$ 143,400,000

Business Overview and Summary of Significant Accounting Policies - Schedule of Balance Sheet Data (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities	$ 1,521.8	$ 1,211.4
Other liabilities - Sanofi	122.4	85.0
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	341.7	310.5
Deferred revenue, noncurrent	16.7	27.7
Other noncurrent liabilities	189.3	482.0
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	236.0	71.6
Deferred revenue, noncurrent	41.1	77.6
Other noncurrent liabilities	$ 497.8	317.7
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities		1,086.8
Other liabilities - Sanofi		0.0
As Previously Reported \| Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		395.5
Deferred revenue, noncurrent		509.7
Other noncurrent liabilities		0.0
As Previously Reported \| Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		196.2
Deferred revenue, noncurrent		109.3
Other noncurrent liabilities		286.0
Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities		124.6
Other liabilities - Sanofi		85.0
Adjustments \| Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		(85.0)
Deferred revenue, noncurrent		(482.0)
Other noncurrent liabilities		482.0
Adjustments \| Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		(124.6)
Deferred revenue, noncurrent		(31.7)
Other noncurrent liabilities		$ 31.7

Business Overview and Summary of Significant Accounting Policies - Schedule of Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 2,422.9	$ 2,294.0	$ 1,952.0	$ 1,828.2	$ 1,863.5	$ 1,743.7	$ 1,577.8	$ 1,372.6	$ 8,497.1	$ 6,557.6	$ 5,145.6
Research and development									2,735.0	2,450.0	1,468.8
Selling, general, and administrative									1,346.0	1,341.9	1,127.2
Cost of Goods and Services Sold										402.8	237.5
Other operating (income) expense, net									(280.4)	(209.2)	(402.3)
Operating expenses	$ 1,255.9	$ 1,240.9	$ 1,295.6	$ 1,128.1	$ 1,187.8	$ 1,005.2	$ 1,262.2	$ 892.6	$ 4,920.5	4,347.8	2,611.2
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										403.6	(125.7)
Bayer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										1,145.6	1,036.1
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										174.0	129.0
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										7,863.4	6,710.8
Research and development										3,036.6	2,186.1
Selling, general, and administrative										1,834.8	1,556.2
Cost of Goods and Services Sold										419.9	254.1
Other operating (income) expense, net										0.0	0.0
Operating expenses										5,653.6	4,176.4
As Previously Reported \| Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										1,426.8	1,111.1
As Previously Reported \| Bayer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										1,188.8	1,076.7
As Previously Reported \| Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										413.4	416.8
Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										(1,305.8)	(1,565.2)
Research and development										(586.6)	(717.3)
Selling, general, and administrative										(492.9)	(429.0)
Cost of Goods and Services Sold										(17.1)	(16.6)
Other operating (income) expense, net										(209.2)	(402.3)
Operating expenses										(1,305.8)	(1,565.2)
Adjustments \| Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										(1,023.2)	(1,236.8)
Adjustments \| Bayer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										(43.2)	(40.6)
Adjustments \| Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										$ (239.4)	$ (287.8)

Business Overview and Summary of Significant Accounting Policies - Schedule of Cash Flows Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in deferred revenue	$ 148.1	$ 139.5	$ (43.4)
Increase in accounts payable, accrued expenses, and other liabilities	$ 118.9	599.0	58.8
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in deferred revenue		294.0	(194.5)
Increase in accounts payable, accrued expenses, and other liabilities		444.5	209.9
Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in deferred revenue		(154.5)	151.1
Increase in accounts payable, accrued expenses, and other liabilities		$ 154.5	$ (151.1)

Business Overview and Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2020
Building and improvements \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Building and improvements \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	50 years
Laboratory equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Laboratory equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years

Product Sales - Schedule of Net Product Sales (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 2,422.9	$ 2,294.0	$ 1,952.0	$ 1,828.2	$ 1,863.5	$ 1,743.7	$ 1,577.8	$ 1,372.6	$ 8,497.1	$ 6,557.6	$ 5,145.6
Product
Disaggregation of Revenue [Line Items]
Revenues									5,567.6	4,834.4	4,106.2
United States \| EYLEA
Disaggregation of Revenue [Line Items]
Revenues									4,947.2	4,644.2	4,076.7
United States \| Libtayo
Disaggregation of Revenue [Line Items]
Revenues									270.7	175.7	14.8
United States \| Praluent
Disaggregation of Revenue [Line Items]
Revenues									150.9
United States \| REGEN-COV
Disaggregation of Revenue [Line Items]
Revenues									185.7	0.0	0.0
United States \| ARCALYST
Disaggregation of Revenue [Line Items]
Revenues									13.1	14.5	14.7
United States \| Product
Disaggregation of Revenue [Line Items]
Revenues									$ 5,567.6	$ 4,834.4	$ 4,106.2

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Product Sales - Schedule of Concentration of Risk, by Risk Factor (Details) - Gross Sales Revenue - Customer concentration risk	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Besse Medical, a subsidiary of AmerisourceBergen Corporation
Concentration Risk [Line Items]
Concentration risk, percentage	51.00%	57.00%	56.00%
McKesson Corporation
Concentration Risk [Line Items]
Concentration risk, percentage	32.00%	33.00%	36.00%

Product Sales - Schedule of Sales Related Deductions Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 156.1	$ 91.4	$ 85.3
Provisions	1,136.9	727.9	478.9
Credits/payments	(968.8)	(663.2)	(472.8)
Ending Balance	324.2	156.1	91.4
Rebates, Chargebacks, and Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	80.3	41.1	29.9
Provisions	762.9	423.2	223.4
Credits/payments	(641.0)	(384.0)	(212.2)
Ending Balance	202.2	80.3	41.1
Distribution- Related Fees
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	46.4	42.0	34.1
Provisions	279.9	242.9	211.0
Credits/payments	(249.1)	(238.5)	(203.1)
Ending Balance	77.2	46.4	42.0
Other Sales- Related Deductions
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	29.4	8.3	21.3
Provisions	94.1	61.8	44.5
Credits/payments	(78.7)	(40.7)	(57.5)
Ending Balance	$ 44.8	$ 29.4	$ 8.3

Collaboration, License, and Other Agreements - Sanofi, Antibody Narrative (Details) - USD ($) $ in Millions		3 Months Ended								9 Months Ended	12 Months Ended
	Apr. 01, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues		$ 2,422.9	$ 2,294.0	$ 1,952.0	$ 1,828.2	$ 1,863.5	$ 1,743.7	$ 1,577.8	$ 1,372.6		$ 8,497.1	$ 6,557.6	$ 5,145.6
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Percentage of quarterly profits require to be paid for reimbursement of development costs											10.00%
Contingent reimbursement obligation		$ 3,103.0									$ 3,103.0
Starting share of profits outside the United States, based on sales, for collaborating party											65.00%
Starting share of profits outside the United States, based on sales, for company											35.00%
Ending share of profits outside the United States, based on sales, for collaborating party											55.00%
Ending share of profits outside the United States, based on sales, for company											45.00%
Share of losses outside the United States, for collaborating party											55.00%
Share of losses outside the United States, for company											45.00%
Levels of twelve month sales at which sales milestone payments would be received										$ 1,000.0	$ 1,500.0
Period for achieving sales target for milestone payment, rolling basis										12 months	12 months
Remaining amount of sales milestone payments if total sales achieve specific levels											$ 200.0
Sanofi Collaboration Agreement, Antibody \| Minimum
Disaggregation of Revenue [Line Items]
Percentage of trial costs required to be funded by collaborating party											80.00%
Percentage of repayment of development balance out of profits											30.00%
Sanofi Collaboration Agreement, Antibody \| Maximum
Disaggregation of Revenue [Line Items]
Percentage of trial costs required to be funded by collaborating party											100.00%
Percentage of repayment of development balance out of profits											50.00%
Sanofi Collaboration Agreement, Antibody \| Sales-based milestone earned
Disaggregation of Revenue [Line Items]
Revenues											$ 50.0	$ 0.0	$ 0.0
Sanofi Collaboration Agreement, Antibody \| Sales-based milestone earned \| First Milestone
Disaggregation of Revenue [Line Items]
Revenues			$ 50.0
Sanofi Collaboration Agreement, Antibody \| Sales-based milestone earned \| Second Milestone
Disaggregation of Revenue [Line Items]
Sales milestone payment if total sales achieve specific levels											$ 50.0
Praluent Agreement
Disaggregation of Revenue [Line Items]
Royalty percentage to be received on net product sales outside of the United States	5.00%
Percentage of damages company is responsible for	50.00%
Praluent Agreement \| Sanofi
Disaggregation of Revenue [Line Items]
Percentage of royalty payment that can be used to offset litigation proceedings	50.00%

Collaboration, License, and Other Agreements - Schedule of Collaboration Revenue Earned From Sanofi (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 2,422.9	$ 2,294.0	$ 1,952.0	$ 1,828.2	$ 1,863.5	$ 1,743.7	$ 1,577.8	$ 1,372.6	$ 8,497.1	$ 6,557.6	$ 5,145.6
Product and service, other \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues
Regeneron's share of profits (losses) in connection with commercialization of antibodies \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									785.2	209.3	(227.0)
Regeneron's share of profits (losses) in connection with commercialization of antibodies \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues									(25.7)	(21.7)	(12.4)
Sales-based milestone earned \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									50.0	0.0	0.0
Reimbursement for manufacturing of commercial supplies \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									368.0	216.0	113.7
Reimbursement for manufacturing of commercial supplies \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues									8.9	0.0	0.0
Reimbursement of research and development expenses \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									226.7	277.7	265.3
Reimbursement of research and development expenses \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues									166.2	163.0	311.8
Regeneron's obligation for its share of Sanofi research and development expenses \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									(77.6)	(46.0)	(47.7)
Reimbursement of commercialization-related expenses \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									359.4	479.9	417.2
Reimbursement of commercialization-related expenses \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues									64.7	10.3	8.9
Regeneron's obligation for its share of Sanofi other expenses \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues									(21.5)	(12.8)	(16.1)
Regeneron's obligation for Sanofi's share of Libtayo U.S. gross profits \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues									(119.1)	(78.2)	(6.8)
Amounts recognized in connection with up-front and development milestone payments received \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues									$ 210.6	$ 92.7	$ 243.8

Collaboration, License, and Other Agreements - Schedule of Accounts Receivable and Deferred Revenue Information, Antibody Collaboration (Details) - Sanofi Collaboration Agreement, Antibody - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 407.7	$ 272.7
Deferred revenue	$ 347.7	$ 328.8

Collaboration, License, and Other Agreements - Sanofi, Immuno-Oncology Narrative (Details) - Sanofi Collaboration Agreement, Immuno-oncology - USD ($)		1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Aug. 31, 2018	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2015
Disaggregation of Revenue [Line Items]
Percentage of quarterly profits require to be paid for reimbursement of development costs					10.00%
Contingent reimbursement obligation					$ 107,000,000
Upfront payment made			$ 20,000,000.0
Remaining performance obligation					557,500,000
Libtayo \| Through December 31, 2023
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid			8.00%
Libtayo \| January 1, 2024 Through December 31, 2026
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid			2.50%
IO Discovery Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received							$ 265,000,000.0
Potential future R&D expenses							1,090,000,000.000
Maximum funding amount of research activities to be reimbursed per agreement							825,000,000.0
BCMAxCD3 Program
Disaggregation of Revenue [Line Items]
Aggregate payment received with regards to amendment				$ 461,900,000
Expenditure costs cap	$ 70,000,000.0
MUC16xCD3 Program
Disaggregation of Revenue [Line Items]
Expenditure costs cap	$ 50,000,000.0
IO License and Collaboration Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received							375,000,000.0
Maximum amount of sales milestone payments if total sales achieve specific levels					375,000,000.0
Period for achieving sales target for milestone payment, rolling basis		12 months
IO License and Collaboration Agreement \| PD-1
Disaggregation of Revenue [Line Items]
Levels of twelve month sales at which sales milestone payments would be received		$ 2,000,000,000.0
IO Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received							$ 640,000,000.0
Amended IO Discovery Agreement \| Other Operating Income (Expense)
Disaggregation of Revenue [Line Items]
Cumulative catch-up adjustment to revenue, modification of contract					$ 135,400,000	$ 135,000,000.0

Collaboration, License, and Other Agreements - Schedule of Accounts Receivable and Deferred Revenue Information, IO Collaboration (Details) - Sanofi Collaboration Agreement, Immuno-oncology - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Accounts receivable, net	$ (6.5)	$ (16.7)
Deferred revenue	10.7	9.4
Other liabilities	$ 280.9	$ 558.6

Collaboration, License, and Other Agreements - Schedule of Collaboration Revenue Earned From Bayer (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 2,422.9	$ 2,294.0	$ 1,952.0	$ 1,828.2	$ 1,863.5	$ 1,743.7	$ 1,577.8	$ 1,372.6	$ 8,497.1	$ 6,557.6	$ 5,145.6
Bayer
Disaggregation of Revenue [Line Items]
Revenues										1,145.6	1,036.1
Bayer \| Product and service, other
Disaggregation of Revenue [Line Items]
Revenues									1,186.1	1,145.6	1,036.1
Outside United States \| Bayer \| Regeneron's net profit in connection with commercialization of EYLEA outside the United States
Disaggregation of Revenue [Line Items]
Revenues									1,107.9	1,091.4	992.3
Outside United States \| Bayer \| Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues									78.2	54.2	43.8
Outside United States \| Bayer \| Reimbursement of development expenses
Disaggregation of Revenue [Line Items]
Revenues									46.7	23.0	11.2
Outside United States \| Bayer \| Regeneron's obligation for its share of Bayer research and development expenses
Disaggregation of Revenue [Line Items]
Revenues									(35.8)	(20.1)	(0.5)
Outside United States \| Bayer \| Reimbursement of other expenses
Disaggregation of Revenue [Line Items]
Revenues									$ 7.4	$ 19.0	$ 28.9

Collaboration, License, and Other Agreements - Bayer Narrative (Details) - Bayer $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Disaggregation of Revenue [Line Items]
Percentage of repayment of development balance out of profits	50.00%
Contingent reimbursement obligation	$ 276
Minimum
Disaggregation of Revenue [Line Items]
Revenue based on percentage of annual sales in Japan	33.50%
Maximum
Disaggregation of Revenue [Line Items]
Revenue based on percentage of annual sales in Japan	40.00%

Collaboration, License, and Other Agreements - Schedule of Contract Balances, Bayer Collaborative (Details) - Bayer - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Accounts receivable - other, net	$ 336.2	$ 311.6
Deferred revenue	$ 99.7	$ 123.0

Collaboration, License, and Other Agreements - Teva Narrative (Details) - Teva - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Up-front payment received			$ 250,000,000.0
Development milestone achieved		$ 60,000,000.0
Aggregate future development milestone payments the Company is eligible to receive	$ 340,000,000.0
Collaborative arrangement, additional eligible aggregate payments	1,890,000,000
Remaining performance obligation	155,900,000
Other Operating Income (Expense)
Disaggregation of Revenue [Line Items]
Cumulative catch-up adjustment to revenue, modification of contract	$ (25,600,000)

Collaboration, License, and Other Agreements - Amounts Recognized in Statement of Operations with Teva (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reimbursement of research and development expenses \| Teva
Disaggregation of Revenue [Line Items]
Reduction of Research and development expense	$ 109.4	$ 122.9	$ 129.5
Amounts recognized in connection with up-front and development milestone payments received
Disaggregation of Revenue [Line Items]
Other operating income	$ 47.2	$ 82.2	$ 113.2

Collaboration, License, and Other Agreements - Schedule of Contract Balances, Teva Collaboration (Details) - Teva - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Accounts receivable - other, net	$ 27.7	$ 21.2
Other liabilities	$ 66.8	$ 114.4

Collaboration, License, and Other Agreements - Intellia Narrative (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Research Collaboration and Licensing Arrangements [Line Items]
Research and development		$ 2,735.0	$ 2,450.0	$ 1,468.8
Intellia Collaboration Agreement
Research Collaboration and Licensing Arrangements [Line Items]
Collaborative Arrangement, Upfront Payment Made	$ 70.0
Research and development	$ 15.0
Intellia Collaboration Agreement \| Common Stock
Research Collaboration and Licensing Arrangements [Line Items]
Shares purchased (in shares)	925,218
Shares purchase price	$ 30.0

Collaboration, License, and Other Agreements - U.S. Government Narrative (Details) - US Government - REGEN-COV - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Maximum transaction agreement payments		$ 465.9
Subsequent Event
Disaggregation of Revenue [Line Items]
Maximum transaction agreement payments	$ 2,625.0

Collaboration, License, and Other Agreements - Roche Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Roche Collaboration Agreement \| REGEN-COV \| Research and Development Expense
Disaggregation of Revenue [Line Items]
Reimbursement of research and development expense	$ 78.5

Collaboration, License, and Other Agreements - Alnylam Narratives (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Aug. 31, 2019	Apr. 30, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Alnylam Pharmaceuticals, Inc. Stock Purchase Agreement
Disaggregation of Revenue [Line Items]
Cash consideration for Stock Purchase Agreement		$ 400.0
Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront payment made			$ 400.0		$ 400.0
Collaborative arrangement additional payment eligible				$ 200.0
Initial research term		5 years
Potential automatic extension of research term		7 years
Potential optional extension of research term		5 years
Maximum amount of sales milestone payments if total sales achieve specific levels	$ 325.0
Minimum \| Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Extension of research term fee		$ 200.0
Maximum \| Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Extension of research term fee		$ 400.0

Marketable Securities - Schedule of Investments in Available For Sale Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 3,649.2	$ 4,206.3
Unrealized Gains	40.1	28.5
Unrealized Losses	(0.2)	(0.3)
Fair Value	3,689.1	4,234.5
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	3,053.0	3,960.5
Unrealized Gains	37.5	27.8
Unrealized Losses	(0.2)	(0.2)
Fair Value	3,090.3	3,988.1
U.S. government and government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	127.6	54.3
Unrealized Gains	1.3	0.2
Unrealized Losses	0.0	(0.1)
Fair Value	128.9	54.4
Sovereign bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	65.2	26.9
Unrealized Gains	1.1	0.4
Unrealized Losses	0.0	0.0
Fair Value	66.3	27.3
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	276.0	92.3
Unrealized Gains	0.1	0.0
Unrealized Losses	0.0	0.0
Fair Value	276.1	92.3
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	127.4	72.3
Unrealized Gains	0.1	0.1
Unrealized Losses	0.0	0.0
Fair Value	$ 127.5	$ 72.4

Marketable Securities - Schedule of Debt Securities Based on Contractual Maturity Dates (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Maturities within one year	$ 1,393.3	$ 1,596.5
Maturities after one year through five years	2,295.8	2,638.0
Total	$ 3,689.1	$ 4,234.5

Marketable Securities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable securities, realized gain	$ 29.0	$ 0.0	$ 0.0
Marketable securities, realized loss	$ 0.0	$ 0.0	$ 0.0

Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Available-for-sale debt securities:
Available-for-sale debt securities	$ 3,689.1	$ 4,234.5
Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Total marketable securities	839.8	618.8
Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Total marketable securities	3,689.1	4,234.5
Unrestricted \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Equity securities	48.3	61.6
Unrestricted \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Equity securities	0.0	0.0
Restricted \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Equity securities	791.5	557.2
Restricted \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Equity securities	0.0	0.0
Estimate of Fair Value Measurement \| Measured on a recurring basis
Available-for-sale debt securities:
Total marketable securities	4,528.9	4,853.3
Estimate of Fair Value Measurement \| Unrestricted \| Measured on a recurring basis
Available-for-sale debt securities:
Equity securities	48.3	61.6
Estimate of Fair Value Measurement \| Restricted \| Measured on a recurring basis
Available-for-sale debt securities:
Equity securities	791.5	557.2
Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	3,090.3	3,988.1
Corporate bonds \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Corporate bonds \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	3,090.3	3,988.1
Corporate bonds \| Estimate of Fair Value Measurement \| Measured on a recurring basis
Available-for-sale debt securities:
Available-for-sale debt securities	3,090.3	3,988.1
U.S. government and government agency obligations
Available-for-sale debt securities:
Available-for-sale debt securities	128.9	54.4
U.S. government and government agency obligations \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
U.S. government and government agency obligations \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	128.9	54.4
U.S. government and government agency obligations \| Estimate of Fair Value Measurement \| Measured on a recurring basis
Available-for-sale debt securities:
Available-for-sale debt securities	128.9	54.4
Sovereign bonds
Available-for-sale debt securities:
Available-for-sale debt securities	66.3	27.3
Sovereign bonds \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Sovereign bonds \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	66.3	27.3
Sovereign bonds \| Estimate of Fair Value Measurement \| Measured on a recurring basis
Available-for-sale debt securities:
Available-for-sale debt securities	66.3	27.3
Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	276.1	92.3
Commercial paper \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Commercial paper \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	276.1	92.3
Commercial paper \| Estimate of Fair Value Measurement \| Measured on a recurring basis
Available-for-sale debt securities:
Available-for-sale debt securities	276.1	92.3
Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	127.5	72.4
Certificates of deposit \| Measured on a recurring basis \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Certificates of deposit \| Measured on a recurring basis \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	127.5	72.4
Certificates of deposit \| Estimate of Fair Value Measurement \| Measured on a recurring basis
Available-for-sale debt securities:
Available-for-sale debt securities	$ 127.5	$ 72.4

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Net unrealized gains (losses) on equity securities in other income (expense)	$ 196.0	$ 118.3	$ (41.9)
Securities without readily determinable fair value	59.2	$ 55.6
Long-term debt fair value	$ 1,958.0

Inventories - Schedule of Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 459.4	$ 216.3
Work-in-process	904.6	727.7
Finished goods	121.7	70.6
Deferred costs	430.9	400.9
Total Inventories	$ 1,916.6	$ 1,415.5

Inventories - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventory write-downs and reserves	$ 39.2	$ 73.8	$ 12.5

Property, Plant, and Equipment - Schedule of Property, Plant, and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	$ 4,352.7	$ 3,812.8
Less, accumulated depreciation and amortization	(1,131.1)	(922.4)
Property, plant, and equipment, net	3,221.6	2,890.4
Land
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	241.2	230.8
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	1,891.1	1,683.4
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	100.5	97.6
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	724.5	644.8
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	1,038.6	850.7
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	226.3	183.7
Furniture, office equipment, and other
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	$ 130.5	$ 121.8

Property, Plant, and Equipment - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 230.8	$ 205.2	$ 144.1
Property, plant, and equipment, net	3,221.6	2,890.4
United States
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	2,398.0	2,118.0
Europe
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	$ 823.8	$ 772.8

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued payroll and related costs	$ 465.8	$ 344.4
Accrued clinical expenses	283.0	142.7
Accrued sales-related charges, deductions, and royalties	423.9	249.0
Income taxes payable	19.5	49.4
Other accrued expenses and liabilities	329.6	425.9
Accrued expenses and other current liabilities	$ 1,521.8	$ 1,211.4

Debt (Details) - USD ($)	1 Months Ended		12 Months Ended
Debt (Details) - USD ($)	Aug. 31, 2020	Dec. 31, 2018	Dec. 31, 2020	May 31, 2020
Bridge Facility \| Common Stock Held By Sanofi \| Bridge Loan
Debt Instrument [Line Items]
Debt, principle amount				$ 1,500,000,000
Line of credit \| Senior unsecured revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 750,000,000.0
Line of credit facility, expiration period		5 years
Increase Limit		$ 250,000,000.0
Borrowings outstanding			$ 0
Line of credit \| Letters of credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 50,000,000.0
Senior unsecured notes
Debt Instrument [Line Items]
Interest expense			$ 17,600,000
Redemption price, percentage	100.00%
Redemption price with change-in-control provision, percentage	101.00%
Senior unsecured notes \| 2030 Notes
Debt Instrument [Line Items]
Debt, principle amount	$ 1,250,000,000
Interest rate	1.75%
Senior unsecured notes \| 2050 Notes
Debt Instrument [Line Items]
Debt, principle amount	$ 750,000,000
Interest rate	2.80%

Commitments and Contingencies - Leases narrative (Details)	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Finance lease, term of contract	5 years
Finance lease, extension option	5 years

Commitments and Contingencies - Amounts recognized in Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Finance lease right-of-use assets	$ 645.7	$ 660.1
Finance lease liabilities	717.2	713.9
Accumulated amortization of right-of-use assets	$ 90.5	$ 76.1
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization

Commitments and Contingencies - Finance lease costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Amortization of right-of-use assets	$ 14.4	$ 14.4
Interest on lease liabilities	15.7	27.6
Finance lease costs	$ 30.1	$ 42.0

Commitments and Contingencies - Other information related to finance lease (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Remaining lease term (in years)	1 year 2 months 1 day	2 years 2 months 1 day
Discount rate	1.66%	3.05%

Commitments and Contingencies - Analysis of lease liability maturities (Details) $ in Millions	Dec. 31, 2020 USD ($)
Finance Leases
2021	$ 12.1
2022	723.1
2023	0.0
2024	0.0
2025	0.0
Thereafter	0.0
Total undiscounted lease payments	735.2
Imputed interest	(15.1)
Debt financing costs	(2.9)
Total lease liabilities	$ 717.2

Commitments and Contingencies - Research Collaboration and Licensing Agreements Narrative (Details) - Agreements with Royalty Provisions - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Research Collaboration and Licensing Arrangements [Line Items]
Royalty rate minimum	0.50%
Royalty rate maximum	11.50%
Royalty expense, net of reimbursements from collaborators	$ 56.5	$ 47.0	$ 30.1

Stockholders' Equity - Narrative (Details)		1 Months Ended	12 Months Ended
Stockholders' Equity - Narrative (Details)	Dec. 31, 2020 USD ($) $ / shares shares	May 31, 2020 USD ($) shares	Dec. 31, 2020 USD ($) vote $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2007 shares	Jan. 31, 2021 USD ($)	Nov. 30, 2019 USD ($)
Class of Stock [Line Items]
Preferred Stock, shares authorized (in shares)	30,000,000		30,000,000	30,000,000
Sanofi
Class of Stock [Line Items]
Cost of stock repurchased \| $		$ 5,000,000,000
Number of shares sold (in shares)		13,014,646
Treasury stock, shares acquired (in shares)		9,806,805
Common Stock, shares outstanding (in shares)		400,000
Sanofi
Class of Stock [Line Items]
Number of shares of common stock purchased (in shares)					12,000,000
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions	30.00%		30.00%
Percentage of outstanding shares or voting rights under amended investor agreement	20.00%		20.00%
Bayer
Class of Stock [Line Items]
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions	20.00%		20.00%
Teva
Class of Stock [Line Items]
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions	5.00%		5.00%
2019 Share Repurchase Program
Class of Stock [Line Items]
Stock repurchase program, authorized amount \| $							$ 1,000,000,000.0
Cost of stock repurchased \| $	$ 1,000,000,000.0		$ 746,000,000.0	$ 254,000,000.0
Treasury stock, shares acquired (in shares)			1,605,582	722,596
2021 Share Repurchase Program \| Subsequent Event
Class of Stock [Line Items]
Stock repurchase program, authorized amount \| $						$ 1,500,000,000
Class A Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares)	40,000,000		40,000,000	40,000,000
Common Stock, par value (in dollars per share) \| $ / shares	$ 0.001		$ 0.001	$ 0.001
Number of votes per share \| vote			10
Common Stock, shares outstanding (in shares)	1,848,970		1,848,970	1,848,970
Common Stock
Class of Stock [Line Items]
Common Stock, shares authorized (in shares)	320,000,000		320,000,000	320,000,000
Common Stock, par value (in dollars per share) \| $ / shares	$ 0.001		$ 0.001	$ 0.001
Number of votes per share \| vote			1

Stockholders' Equity - Schedule of Repurchased Shares (Details) - 2019 Share Repurchase Program - USD ($)		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares acquired (in shares)		1,605,582	722,596
Total cost of shares received	$ 1,000,000,000.0	$ 746,000,000.0	$ 254,000,000.0

Stockholders' Equity - Sanofi Funding (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Libtayo
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares acquired (in shares)	77,677	210,733	215,387
Total cost of shares received	$ 41.7	$ 73.3	$ 75.8
Dupilumab/Itepekimab
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares acquired (in shares)	171,471	93,286	10,766
Total cost of shares received	$ 93.3	$ 29.4	$ 4.4

Long-Term Incentive Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of awards	10 years
Total intrinsic value - of stock options exercised	$ 2,251.0	$ 558.9	$ 510.6
Expected dividend yield	0.00%	0.00%	0.00%
Stock options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Stock options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Non-performance based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 329.5	$ 422.8	$ 421.8
Capitalized to inventory	8.3	2.4	17.1
Unrecognized stock-based compensation cost, net of estimated forfeitures	$ 491.5
Weighted average period for recognition of total unrecognized compensation expense (in years)	1 year 9 months 18 days
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 102.5	29.7	$ 5.6
Unrecognized stock-based compensation cost, net of estimated forfeitures	$ 425.5
Weighted average period for recognition of total unrecognized compensation expense (in years)	2 years 8 months 12 days
Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
Non-cash stock-based compensation expense	$ 0.0	$ 11.7
Unrecognized stock-based compensation cost, net of estimated forfeitures	$ 260.0
Weighted average period for recognition of total unrecognized compensation expense (in years)	5 years
Expected dividend yield	0.00%	0.00%
Performance-based stock options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance threshold, target number of awards granted, percent	0.00%
Performance-based stock options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance threshold, target number of awards granted, percent	250.00%
Amended & Restated Long-Term Incentive Plan 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares registered (in shares)				12,000,000
Number of shares authorized for issuance (in shares)				22,269,970
Number of shares available for future grants (in shares)	18,916,095
Long-Term Incentive Plan 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grants (in shares)	0
Long-Term Incentive Plan 2000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grants (in shares)	0

Long-Term Incentive Plans - Summary of transactions involving stock option awards (Details) - Stock options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Outstanding at beginning of period (in shares)	28,609,277,000
Granted (in shares)	2,850,590,000	3,271,222,000	4,665,320,000
Forfeited (in shares)	(562,629,000)
Expired (in shares)	(56,282,000)
Exercised (in shares)	(9,139,287,000)
Outstanding at end of period (in shares)	21,701,669,000	28,609,277,000
Vested and expected to vest (in shares)	20,764,534,000
Exercisable (in shares)	13,648,899,000
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 337.24
Granted (in dollars per share)	492.60	$ 366.65	$ 378.51
Forfeited (in dollars per share)	379.02
Expired (in dollars per share)	473.77
Exercised (in dollars per share)	281.90
Outstanding at end of period (in dollars per share)	379.51	$ 337.24
Vested and expected to vest (in dollars per share)	377.23
Exercisable (in dollars per share)	$ 357.65
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term (in years) - outstanding	6 years 4 months 2 days
Weighted average remaining contractual term - vested and expected to vest	6 years 2 months 19 days
Weighted average remaining contractual term - exercisable	4 years 11 months 15 days
Intrinsic value - outstanding	$ 2,347.4
Intrinsic value - vested and expected to vest	2,294.1
Intrinsic value - exercisable	$ 1,799.1

Long-Term Incentive Plans - Summary of weighted-average exercise prices and weighted-average grant-date fair values of options issued (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options Granted (in shares)	2,850,590,000	3,271,222,000	4,665,320,000
Weighted-Average Exercise Price (in dollars per share)	$ 492.60	$ 366.65	$ 378.51
Weighted-Average Fair Value (in dollars per share)	$ 126.50	$ 100.80	$ 114.39

Long-Term Incentive Plans - Summary of weighted-average values of assumptions used in computing fair value of option grants (Details) - Stock options	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	28.00%	28.00%	29.00%
Expected lives from grant date	5 years	5 years	4 years 10 months 24 days
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate	0.47%	1.74%	2.69%

Long-Term Incentive Plans - Summary of activity related to restricted stock awards (Details) - Restricted stock	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Number of Shares/Units
Beginning balance (in shares) \| shares	1,102,390
Granted (in shares) \| shares	646,844
Vested (in shares) \| shares	(15,630)
Forfeited/Cancelled (in shares) \| shares	(46,061)
Ending balance (in shares) \| shares	1,687,543
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars of shares) \| $ / shares	$ 377.32
Granted (in dollars of shares) \| $ / shares	496.44
Vested (in dollars of shares) \| $ / shares	526.62
Forfeited/Cancelled (in dollars of shares) \| $ / shares	377.85
Ending balance (in dollars of shares) \| $ / shares	$ 421.58

Long-Term Incentive Plans - Summary of activity related to performance-based stock awards (Details) - Performance-based stock options	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Number of Shares/Units
Beginning balance (in shares) \| shares	59,396
Granted (in shares) \| shares	1,240,540
Vested (in shares) \| shares	0
Forfeited/Cancelled (in shares) \| shares	0
Ending balance (in shares) \| shares	1,299,936
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars of shares) \| $ / shares	$ 198.10
Granted (in dollars of shares) \| $ / shares	209.59
Vested (in dollars of shares) \| $ / shares	0
Forfeited/Cancelled (in dollars of shares) \| $ / shares	0
Ending balance (in dollars of shares) \| $ / shares	$ 209.06

Long-Term Incentive Plans - Summary of weighted-average values of assumptions used in computing fair value of performance-based options (Details) - Performance-based stock options	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	35.00%	33.00%
Expected dividend yield	0.00%	0.00%
Risk-free interest rate	0.36%	1.63%

Employee Savings Plans (Details) - USD ($) $ in Millions	12 Months Ended
Employee Savings Plans (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Employer contribution expense to 401(k) Savings Plan	$ 44.7	$ 38.1	$ 27.0

Income Taxes - Schedule of income before income tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income before income taxes, United States	$ 2,442.3	$ 2,011.2	$ 2,151.7
Income before income taxes, Foreign	1,368.1	417.9	401.8
Income before income taxes	$ 3,810.4	$ 2,429.1	$ 2,553.5

Income Taxes - Schedule of components of income tax expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 199.0	$ 444.6	$ 223.7
State	1.2	1.9	4.8
Foreign	21.4	(2.6)	20.6
Total current tax expense	221.6	443.9	249.1
Deferred:
Federal	109.0	(132.0)	687.6
State	(2.0)	(1.7)	(1.9)
Foreign	(31.4)	3.1	(825.7)
Total deferred tax (benefit) expense	75.6	(130.6)	(140.0)
Total income tax expense (benefit)	$ 297.2	$ 313.3	$ 109.1

Income Taxes - Schedule of effective income tax rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	21.00%	21.00%	21.00%
Stock-based compensation	(7.60%)	(2.50%)	(2.50%)
Income tax credits	(2.80%)	(4.60%)	(2.60%)
Taxation of non-U.S. operations	(1.80%)	(1.00%)	(1.90%)
Sale of non-inventory related assets between foreign subsidiaries	0.80%	0.00%	6.30%
Foreign-derived intangible income deduction	0.00%	(1.60%)	(1.00%)
Non-deductible Branded Prescription Drug Fee	0.50%	0.70%	0.60%
Impact of change in U.S. corporate tax rate (the Act)	0.00%	0.00%	(2.70%)
Other permanent differences	(0.70%)	0.90%	(0.30%)
Effective income tax rate	7.80%	12.90%	4.30%

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate	7.80%	12.90%	4.30%
U.S. federal statutory tax rate	21.00%	21.00%	21.00%
Adjustment to provisional amount recorded			$ 68.0
Unrecognized tax benefits that would impact effective tax rate		$ 210.8	$ 189.5

Income Taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Deferred compensation	$ 436.6	$ 519.7
Fixed assets and intangible assets	140.5	192.0
Accrued expenses	139.8	75.9
Deferred revenue	44.6	22.0
Total deferred tax assets	761.5	809.6
Valuation allowance	0.0	(7.0)
Deferred tax assets, net of valuation allowance	761.5	802.6
Deferred tax liabilities:
Other	(42.8)	(11.2)
Net deferred tax assets	$ 718.7	$ 791.4

Income Taxes - Schedule of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of January 1	$ 210.8	$ 189.5	$ 146.2
Gross increases related to current year tax positions	76.6	37.9	51.4
Gross increases related to prior year tax positions	7.2		5.6
Gross decreases related to prior year tax positions		(7.2)
Gross decreases due to settlements and lapse of statutes of limitations	(27.6)	(9.4)	(13.7)
Balance as of December 31	$ 267.0	$ 210.8	$ 189.5

Legal Matters (Details) $ in Millions	Jul. 16, 2020 claim	Jul. 31, 2017 claim	Sep. 26, 2016 EUR (€)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Feb. 25, 2019 claim	Feb. 14, 2019 claim
Loss Contingencies [Line Items]
Accruals for loss contingencies \| $				$ 9.6	$ 100.0
Amgen v.s. Regeneron \| Pending Litigation
Loss Contingencies [Line Items]
Loss contingency, damages sought, per unit produced \| €			€ 10,000
Loss contingency, damages sought \| €			€ 10,000,000.0
'165 Patent \| Amgen v.s. Regeneron \| Pending Litigation
Loss Contingencies [Line Items]
Pending claims						2
Invalid claims						2
'741 Patent \| Amgen v.s. Regeneron \| Pending Litigation
Loss Contingencies [Line Items]
Pending claims						1
'487 Patent
Loss Contingencies [Line Items]
Number of IPR filed		2
Number of claims invalidated							17
'631 Patent
Loss Contingencies [Line Items]
Number of IPR filed	2

Net Income Per Share - Schedule of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income - basic and diluted	$ 1,149.2	$ 842.1	$ 897.3	$ 624.6	$ 792.0	$ 669.6	$ 193.1	$ 461.1	$ 3,513.2	$ 2,115.8	$ 2,444.4
Weighted average shares outstanding - basic (in shares)									107.6	109.2	107.9
Effect of dilutive securities:
Weighted average shares - diluted (in shares)									115.1	114.6	114.8
Net income per share - basic (in dollars per share)	$ 10.90	$ 7.98	$ 8.19	$ 5.69	$ 7.25	$ 6.12	$ 1.77	$ 4.23	$ 32.65	$ 19.38	$ 22.65
Net income per share - diluted (in dollars per share)	$ 10.24	$ 7.39	$ 7.61	$ 5.43	$ 6.93	$ 5.86	$ 1.68	$ 3.99	$ 30.52	$ 18.46	$ 21.29
Stock options
Effect of dilutive securities:
Effect of dilutive securities (in shares)									7.0	5.4	6.9
Restricted stock
Effect of dilutive securities:
Effect of dilutive securities (in shares)									0.5	0.0	0.0

Net Income Per Share - Schedule of Antidilutive Securities Excluded From Computation (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares (in shares)	2.7	18.4	14.9

Statement of Cash Flows - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 2,193.7	$ 1,617.8	$ 1,467.7
Restricted cash included in Other noncurrent assets	13.6	12.5	12.5
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statement of Cash Flows	$ 2,207.3	$ 1,630.3	$ 1,480.2	$ 825.2

Statement of Cash Flows - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Accrued capital expenditures	$ 83.6	$ 133.7	$ 54.5

Unaudited Quarterly Results - Schedule of unaudited quarterly results (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 2,422.9	$ 2,294.0	$ 1,952.0	$ 1,828.2	$ 1,863.5	$ 1,743.7	$ 1,577.8	$ 1,372.6	$ 8,497.1	$ 6,557.6	$ 5,145.6
Operating expenses	1,255.9	1,240.9	1,295.6	1,128.1	1,187.8	1,005.2	1,262.2	892.6	4,920.5	4,347.8	2,611.2
Net income	$ 1,149.2	$ 842.1	$ 897.3	$ 624.6	$ 792.0	$ 669.6	$ 193.1	$ 461.1	$ 3,513.2	$ 2,115.8	$ 2,444.4
Net income per share - basic (in dollars per share)	$ 10.90	$ 7.98	$ 8.19	$ 5.69	$ 7.25	$ 6.12	$ 1.77	$ 4.23	$ 32.65	$ 19.38	$ 22.65
Net income per share - diluted (in dollars per shares)	$ 10.24	$ 7.39	$ 7.61	$ 5.43	$ 6.93	$ 5.86	$ 1.68	$ 3.99	$ 30.52	$ 18.46	$ 21.29
Amgen v.s. Regeneron
Disaggregation of Revenue [Line Items]
Reversal of accruals for litigation-related contingencies	$ 95.0
Intellia Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront payment made			$ 85.0
Sanofi IO, Teva and MTPC Collaboration Agreements
Disaggregation of Revenue [Line Items]
Cumulative catch-up adjustment to revenue, modification of contract	$ 99.8
Alnylam Pharmaceuticals, Inc. Collaboration Agreement
Disaggregation of Revenue [Line Items]
Upfront payment made							$ 400.0			$ 400.0