Collaboration, License, and Other Agreements - Schedule of Collaboration Revenue Earned From Bayer (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 16,071.7	$ 8,497.1	$ 6,557.6
Outside United States | Bayer | Collaboration revenue | Regeneron's net profit in connection with commercialization of EYLEA outside the United States
Disaggregation of Revenue [Line Items]
Revenues	1,349.2	1,107.9	1,091.4
Outside United States | Bayer | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	60.1	78.2	54.2
Outside United States | Bayer | Research and development expense | Reimbursement of development expenses
Disaggregation of Revenue [Line Items]
Revenues	46.1	46.7	23.0
Outside United States | Bayer | Research and development expense | Regeneron's obligation for its share of Bayer research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	$ (40.9)	$ (35.8)	$ (20.1)