Collaboration, License, and Other Agreements - Amounts Recognized In Statement of Operations with Sanofi (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues	$ 3,675.6	$ 3,547.1	$ 6,704.3	$ 6,692.1
Sanofi Collaboration Agreement, Antibody \| Collaboration revenue \| Regeneron's share of profits
Disaggregation of Revenue [Line Items]
Revenues	1,282.1	988.3	2,300.2	1,792.3
Sanofi Collaboration Agreement, Antibody \| Collaboration revenue \| Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	161.5	157.3	326.6	263.1
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	(18.0)	(9.1)	(33.5)	(27.7)
Sanofi Collaboration Agreement, Antibody \| Reduction of SG&A expense \| Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	$ 194.0	$ 150.8	$ 353.2	$ 290.3