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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 3,720.7	$ 3,362.7	$ 10,412.8	$ 9,682.9
Sanofi Collaboration Agreement, Antibody \| Collaboration revenue \| Regeneron's share of profits
Disaggregation of Revenue [Line Items]
Revenues	1,088.3	863.0	2,880.6	2,250.6
Sanofi Collaboration Agreement, Antibody \| Collaboration revenue \| Sales-based milestones earned
Disaggregation of Revenue [Line Items]
Revenues	0.0	50.0	0.0	50.0
Sanofi Collaboration Agreement, Antibody \| Collaboration revenue \| Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	175.1	151.5	438.2	506.0
Sanofi Collaboration Agreement, Antibody \| (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	(7.8)	(25.8)	(35.5)	(66.7)
Sanofi Collaboration Agreement, Antibody \| Reduction of SG&A expense \| Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	$ 169.0	$ 135.5	$ 459.3	$ 384.0