Revenues - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) wholesaler	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) wholesaler	Sep. 30, 2022 USD ($)
Disaggregation of Revenue [Line Items]
Number of wholesalers | wholesaler	2		2
Product revenues	$ 2,530.3	$ 2,508.5	$ 7,449.3	$ 7,629.4
Selling, general and administrative	$ 788.2	$ 563.3	$ 1,941.2	$ 1,770.8
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenues from major distributors	26.90%	26.90%	27.10%	26.80%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenues from major distributors	10.50%	10.50%	9.10%	10.70%
Contract manufacturing, royalty and other revenue
Disaggregation of Revenue [Line Items]
Product revenues	$ 304.2	$ 129.5	$ 781.2	$ 293.5
LEQEMBI Collaboration
Disaggregation of Revenue [Line Items]
Share of non-controling interest recognized	50.00%		50.00%
Selling, general and administrative	$ 38.7