Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 107.9	$ 77.0
Expense reflected within statements of income	54.0	38.5
Selling, general and administrative | E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	5.3	8.0
Expense incurred by the collaboration	$ 10.5	15.9
Selling, general and administrative | ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income		50.9
Expense incurred by the collaboration		$ 95.0