v3.10.0.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2018
Jan. 31, 2019
Jun. 29, 2018
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, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Emerging Growth Company false    
Entity Small Business false    
Entity Shell Company false    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 35,741,000,000
Common Stock      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   107,365,835  
Class A Stock      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   1,911,354