Product Sales - Schedule of Net Product Sales (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 2,294.0	$ 1,743.7	$ 6,074.2	$ 4,694.1
Product
Disaggregation of Revenue [Line Items]
Revenues	1,482.2	1,238.3	3,945.8	3,548.0
UNITED STATES | Product
Disaggregation of Revenue [Line Items]
Revenues	1,482.2	1,238.3	3,945.8	3,548.0
UNITED STATES | EYLEA
Disaggregation of Revenue [Line Items]
Revenues	1,318.3	1,187.7	3,604.0	3,422.1
UNITED STATES | Libtayo
Disaggregation of Revenue [Line Items]
Revenues	71.6	47.6	196.6	115.2
UNITED STATES | Praluent
Disaggregation of Revenue [Line Items]
Revenues	48.5		95.7
UNITED STATES | REGN-COV2
Disaggregation of Revenue [Line Items]
Revenues	40.2	0.0	40.2	0.0
UNITED STATES | ARCALYST
Disaggregation of Revenue [Line Items]
Revenues	$ 3.6	$ 3.0	$ 9.3	$ 10.7