Collaboration and License Agreements - Schedule of Collaboration Revenue Earned From Bayer (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 1,927.8	$ 1,663.5	$ 1,608.0	$ 1,511.5	$ 1,582.4	$ 1,500.7	$ 1,470.1	$ 1,319.0	$ 6,710.8	$ 5,872.2	$ 4,860.4
Bayer | Product and service, other
Disaggregation of Revenue [Line Items]
Revenues									1,076.7	938.1	744.3
Outside United States | Bayer | Product and service, other
Disaggregation of Revenue [Line Items]
Revenues									1,077.1	874.3	710.8
Outside United States | Bayer | Net profit in connection with commercialization
Disaggregation of Revenue [Line Items]
Revenues									992.3	802.3	649.2
Outside United States | Bayer | Reimbursement of Regeneron research and development expenses
Disaggregation of Revenue [Line Items]
Revenues									11.2	13.3	9.0
Outside United States | Bayer | Other
Disaggregation of Revenue [Line Items]
Revenues									$ 73.6	$ 58.7	$ 52.6