Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - E2609 and BAN2401 - Eisai - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 90.6	$ 86.2	$ 177.9	$ 194.1
Expense reflected within statements of income	45.4	43.0	89.0	97.0
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	68.9	8.5	155.8	13.8
Expense incurred by the collaboration	$ 137.7	$ 17.1	$ 311.6	$ 27.6