Collaborative and Other Relationships - Summary of Activity Related to LEQEMBI Collaboration (Details) - LEQEMBI - LEQEMBI Collaboration - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	$ 164.8	$ 186.0	$ 173.6
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	329.6	371.9	347.2
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	323.5	152.2	52.3
Expense incurred by the collaboration	$ 647.0	$ 304.4	$ 104.6