Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 371.9	$ 347.2	$ 323.0
Expense reflected within statements of income	186.0	173.6	161.5
Selling, general and administrative | E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	152.2	52.3	13.6
Expense incurred by the collaboration	$ 304.4	$ 104.6	$ 27.2