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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 2,857.2	$ 5,138.5	$ 5,822.3	$ 7,667.2
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Regeneron's share of profits (losses) in connection with commercialization
Disaggregation of Revenue [Line Items]
Revenues	496.6	327.6	911.9	588.2
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Sales-based milestone earned
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	50.0	0.0
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	145.5	110.9	306.3	216.5
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Other
Disaggregation of Revenue [Line Items]
Revenues	28.9	0.0	28.9	0.0
Sanofi Collaboration Agreement, Antibody | Research and development expense | Reimbursement of research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	52.7	46.5	89.2	77.1
Sanofi Collaboration Agreement, Antibody | Research and development expense | Regeneron's obligation for its share of Sanofi research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	(15.6)	(10.6)	(25.3)	(22.5)
Sanofi Collaboration Agreement, Antibody | Selling, general and administrative expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	110.8	78.3	202.5	137.9
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Regeneron's share of profits (losses) in connection with commercialization | Outside United States
Disaggregation of Revenue [Line Items]
Revenues	3.9	(3.5)	6.7	(9.6)
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Reimbursement for manufacturing of ex-U.S. commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	2.6	2.7	4.6	7.4
Sanofi Collaboration Agreement, Immuno-oncology | Research and development expense | Reimbursement of research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	21.2	22.5	42.7	44.4
Sanofi Collaboration Agreement, Immuno-oncology | Selling, general and administrative expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	22.4	20.7	41.4	39.2
Sanofi Collaboration Agreement, Immuno-oncology | Selling, general and administrative expense | Regeneron's obligation for its share of Sanofi commercial expenses
Disaggregation of Revenue [Line Items]
Revenues	(10.7)	(10.9)	(19.9)	(18.6)
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	(37.8)	(34.4)	(70.1)	(64.8)
Sanofi Collaboration Agreement, Immuno-oncology | Other operating income | Amounts recognized in connection with up-front payments received
Disaggregation of Revenue [Line Items]
Revenues	$ 17.0	$ 20.7	$ 35.1	$ 43.6