v3.3.1.900
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2015
Feb. 04, 2016
Jun. 30, 2015
Entity Information [Line Items]      
Entity Registrant Name REGENERON PHARMACEUTICALS INC    
Entity Central Index Key 0000872589    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Document Type 10-K    
Document Period End Date Dec. 31, 2015    
Document Fiscal Year Focus 2015    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 50,626,000,000
Common Stock      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   102,874,369  
Class A Stock      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   1,913,776