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, 2025	Mar. 31, 2024
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	$ 26.3	$ 43.6
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	52.6	87.3
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	88.8	86.9
Expense incurred by the collaboration	$ 177.7	$ 173.9