Product Sales - Schedule of Net Product Sales (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Revenue [Line Items]
Revenues	$ 4,290.7	$ 3,675.6	$ 7,896.1	$ 6,704.3
Net product sales
Disaggregation of Revenue [Line Items]
Revenues	1,642.4	1,631.0	3,176.9	3,046.6
Libtayo
Disaggregation of Revenue [Line Items]
Revenues	489.4	376.5	927.6	661.6
Other products
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	31.3	0.0
Lynozyfic
Disaggregation of Revenue [Line Items]
Revenues	16.5	0.0	27.7	0.0
U.S. \| EYLEA HD And EYLEA
Disaggregation of Revenue [Line Items]
Revenues	1,008.5	1,147.5	1,950.0	2,190.3
U.S. \| EYLEA HD
Disaggregation of Revenue [Line Items]
Revenues	596.3	393.2	1,064.7	700.0
U.S. \| EYLEA
Disaggregation of Revenue [Line Items]
Revenues	412.2	754.3	885.3	1,490.3
U.S. \| Libtayo
Disaggregation of Revenue [Line Items]
Revenues	342.6	247.8	628.7	440.3
U.S. \| Praluent
Disaggregation of Revenue [Line Items]
Revenues	74.7	65.8	141.3	122.6
U.S. \| Evkeeza
Disaggregation of Revenue [Line Items]
Revenues	53.3	41.2	99.0	72.1
Rest Of World \| Libtayo
Disaggregation of Revenue [Line Items]
Revenues	$ 146.8	$ 128.7	$ 298.9	$ 221.3