Collaboration Agreements - Schedule of Collaboration Revenue Earned From Bayer (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 1,933.7	$ 1,608.0	$ 3,645.5	$ 3,119.5
Bayer | Product and service, other
Disaggregation of Revenue [Line Items]
Revenues	289.0	262.9	565.2	510.8
Outside United States | Bayer | Product and service, other
Disaggregation of Revenue [Line Items]
Revenues	289.0	262.7	565.2	510.1
Outside United States | Bayer | Net profit in connection with commercialization
Disaggregation of Revenue [Line Items]
Revenues	269.0	246.3	518.3	478.4
Outside United States | Bayer | Reimbursement of Regeneron research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	8.0	3.7	10.6	7.1
Outside United States | Bayer | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 12.0	$ 12.7	$ 36.3	$ 24.6