Collaboration, License, and Other Agreements - Amounts Recognized In Statement of Operations with Sanofi (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 2,936.2	$ 3,452.8	$ 8,758.5	$ 11,120.0
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Regeneron's share of profits (losses) in connection with commercialization
Disaggregation of Revenue [Line Items]
Revenues	551.1	387.0	1,463.0	975.2
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Sales-based milestone earned
Disaggregation of Revenue [Line Items]
Revenues	0.0	50.0	50.0	50.0
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	160.5	144.7	466.8	361.2
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Other
Disaggregation of Revenue [Line Items]
Revenues	(0.2)	0.0	28.7	0.0
Sanofi Collaboration Agreement, Antibody | (R&D expense)/reduction of R&D expense | (Regeneron's obligation for its share of Sanofi R&D expenses)/reimbursements of R&D expenses, net
Disaggregation of Revenue [Line Items]
Revenues	(4.3)	34.9	59.6	89.5
Sanofi Collaboration Agreement, Antibody | Selling, general and administrative expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	108.6	79.0	311.1	216.9
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Regeneron's share of profits (losses) in connection with commercialization | Outside United States
Disaggregation of Revenue [Line Items]
Revenues	0.0	(3.0)	6.7	(12.6)
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Reimbursement for manufacturing of ex-U.S. commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	0.0	3.1	4.6	10.5
Sanofi Collaboration Agreement, Immuno-oncology | (R&D expense)/reduction of R&D expense | Reimbursement of R&D expenses
Disaggregation of Revenue [Line Items]
Revenues	0.0	21.8	42.7	66.2
Sanofi Collaboration Agreement, Immuno-oncology | Selling, general and administrative expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	0.0	22.8	41.4	62.0
Sanofi Collaboration Agreement, Immuno-oncology | Selling, general and administrative expense | Regeneron's obligation for its share of Sanofi commercial expenses
Disaggregation of Revenue [Line Items]
Revenues	0.0	(9.4)	(19.9)	(28.0)
Sanofi Collaboration Agreement, Immuno-oncology | Cost of goods sold | Regeneron's obligation for Sanofi's share of Libtayo U.S. gross profits
Disaggregation of Revenue [Line Items]
Revenues	0.0	(34.6)	(70.1)	(99.4)
Sanofi Collaboration Agreement, Immuno-oncology | Other operating income | Amounts recognized in connection with up-front payments received
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0	$ (47.7)	$ 35.1	$ (4.1)