Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 01, 2017	Jun. 30, 2016
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, 2016
Document Fiscal Year Focus	2016
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			$ 35,224,000,000
Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		104,169,299
Class A Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,911,456