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, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues	$ 3,754.3	$ 3,720.7	$ 10,458.6	$ 10,412.8
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Regeneron's share of profits
Disaggregation of Revenue [Line Items]
Revenues	1,455.5	1,088.3	3,755.7	2,880.6
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	161.5	175.1	488.1	438.2
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	(23.5)	(7.8)	(56.9)	(35.5)
Sanofi Collaboration Agreement, Antibody | Reduction of SG&A expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	$ 182.6	$ 169.0	$ 535.8	$ 459.3