Collaboration and License Agreements - Schedule of Collaboration Revenue Earned From Bayer (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 2,169.5	$ 2,048.4	$ 1,933.7	$ 1,711.8	$ 1,927.8	$ 1,663.5	$ 1,608.0	$ 1,511.5	$ 7,863.4	$ 6,710.8	$ 5,872.2
Bayer | Product and service, other
Disaggregation of Revenue [Line Items]
Revenues									1,188.8	1,076.7	938.1
Outside United States | Bayer | Product and service, other
Disaggregation of Revenue [Line Items]
Revenues									1,188.8	1,077.1	874.3
Outside United States | Bayer | Regeneron's net profit in connection with commercialization of EYLEA outside the United States
Disaggregation of Revenue [Line Items]
Revenues									1,091.4	992.3	802.3
Outside United States | Bayer | Reimbursement of EYLEA development expenses
Disaggregation of Revenue [Line Items]
Revenues									23.0	11.2	13.3
Outside United States | Bayer | Other
Disaggregation of Revenue [Line Items]
Revenues									$ 74.4	$ 73.6	$ 58.7