Collaboration, License, and Other Agreements - Amounts Recognized in Statement of Operations with Bayer (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
Bayer | Rest Of World | Collaboration revenue | Regeneron's share of profits
Disaggregation of Revenue [Line Items]
Revenues	311.9	367.6	1,012.6	1,054.5
Bayer | Rest Of World | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	32.9	23.2	91.1	67.4
Bayer | Rest Of World | (R&D expense) | Regeneron's obligation for its share of Bayer R&D expenses, net of reimbursement of R&D expenses
Disaggregation of Revenue [Line Items]
Revenues	$ (3.9)	$ (11.8)	$ (18.9)	$ (35.2)