Revenue - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) wholesaler	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Disaggregation of Revenue [Line Items]
Number of wholesalers | wholesaler	2
Percentage of total revenues	18.80%	18.10%	17.20%
Revenue	$ 9,890.6	$ 9,675.9	$ 9,835.6
LEQEMBI Collaboration
Disaggregation of Revenue [Line Items]
Share of non-controling interest recognized	50.00%
Alzheimer's collaboration revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 177.7	$ 59.9	$ 0.0
Distributor One
Disaggregation of Revenue [Line Items]
Percentage receivables of wholesale distributor accounted in consolidated receivables	25.40%	27.20%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage receivables of wholesale distributor accounted in consolidated receivables	15.20%	11.70%
Distributor One
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors	28.00%	25.90%	27.00%
Distributor Two
Disaggregation of Revenue [Line Items]
Percentage of revenue from major distributors	15.80%	13.40%	9.90%