Collaboration, License, and Other Agreements - Schedule of Collaboration Revenue Earned From Sanofi (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 13,117.2	$ 12,172.9	$ 16,071.7
One-time payment		(56.9)
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Regeneron's share of profits in connection with commercialization of antibodies
Disaggregation of Revenue [Line Items]
Revenues	3,136.5	2,082.0	1,363.0
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Sales-based milestones earned
Disaggregation of Revenue [Line Items]
Revenues	50.0	100.0	50.0
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	613.0	633.7	488.8
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Other
Disaggregation of Revenue [Line Items]
Revenues	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, net of reimbursement of R&D expenses
Disaggregation of Revenue [Line Items]
Revenues	(83.7)	43.0	129.2
Sanofi Collaboration Agreement, Antibody | SG&A expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	534.4	437.4	320.5
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Regeneron's share of profits in connection with commercialization of antibodies
Disaggregation of Revenue [Line Items]
Revenues	0.0	6.7	(13.6)
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	0.0	4.6	14.0
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	42.7	85.1
Sanofi Collaboration Agreement, Immuno-oncology | SG&A expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	0.0	41.4	89.6
Sanofi Collaboration Agreement, Immuno-oncology | SG&A expense | Regeneron's obligation for its share of Sanofi commercial expenses
Disaggregation of Revenue [Line Items]
Revenues	0.0	(19.9)	(36.3)
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	(70.1)	(133.0)
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	$ 35.1	$ 6.1