Revenues - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) wholesaler	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) wholesaler	Jun. 30, 2022 USD ($)
Disaggregation of Revenue [Line Items]
Number of wholesalers | wholesaler	2		2
Product revenues	$ 2,456.0	$ 2,589.1	$ 4,919.0	$ 5,120.9
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenues from major distributors	27.00%	27.40%	27.20%	26.80%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenues from major distributors	9.30%	11.20%	8.40%	10.80%
Contract manufacturing, royalty and other revenue
Disaggregation of Revenue [Line Items]
Product revenues	$ 197.5	$ 97.9	$ 516.6	$ 164.0
LEQEMBI Collaboration
Disaggregation of Revenue [Line Items]
Product revenues	$ (20.7)	$ 0.0	$ (39.6)	$ 0.0