Collaborative and Other Relationships - Summary of Activity Related to LEQEMBI Collaboration (Details) - LEQEMBI - Alzheimer's collaboration revenue - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 69.3	$ 52.6
Expense reflected within statements of income	34.6	26.3
Selling, General and Administrative Expenses [Member]
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	84.7	88.8
Expense incurred by the collaboration	$ 169.5	$ 177.7