Collaboration, License, and Other Agreements - Schedule of Collaboration Revenue Earned From Sanofi (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 16,071.7	$ 8,497.1	$ 6,557.6
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Regeneron's share of profits in connection with commercialization of antibodies
Disaggregation of Revenue [Line Items]
Revenues	1,363.0	785.2	209.3
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Sales-based milestones earned
Disaggregation of Revenue [Line Items]
Revenues	50.0	50.0	0.0
Sanofi Collaboration Agreement, Antibody | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	488.8	368.0	216.0
Sanofi Collaboration Agreement, Antibody | Research and development expense | Reimbursement of research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	175.9	226.7	277.7
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	(46.7)	(77.6)	(46.0)
Sanofi Collaboration Agreement, Antibody | Selling, general, and administrative expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	320.5	359.4	479.9
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Regeneron's share of profits in connection with commercialization of antibodies
Disaggregation of Revenue [Line Items]
Revenues	(13.6)	(25.7)	(21.7)
Sanofi Collaboration Agreement, Immuno-oncology | Collaboration revenue | Reimbursement for manufacturing of commercial supplies
Disaggregation of Revenue [Line Items]
Revenues	14.0	8.9	0.0
Sanofi Collaboration Agreement, Immuno-oncology | Research and development expense | Reimbursement of research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	85.1	166.2	163.0
Sanofi Collaboration Agreement, Immuno-oncology | Selling, general, and administrative expense | Reimbursement of commercialization-related expenses
Disaggregation of Revenue [Line Items]
Revenues	89.6	64.7	10.3
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	(36.3)	(22.4)	(15.4)
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	(133.0)	(119.1)	(78.2)
Sanofi Collaboration Agreement, Immuno-oncology | Other operating income | Amounts recognized in connection with up-front and development milestone payments received
Disaggregation of Revenue [Line Items]
Revenues	$ 6.1	$ 210.6	$ 92.7