Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 86.2	$ 78.6	$ 194.1	$ 155.6
Expense reflected within statements of income	43.0	39.3	97.0	77.8
Selling, general and administrative | E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	8.5	11.7	13.8	19.7
Expense incurred by the collaboration	$ 17.1	23.4	$ 27.6	39.3
Selling, general and administrative | ADUHELM
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income		21.1		72.0
Expense incurred by the collaboration		$ 40.8		$ 135.8