Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - E2609 and BAN2401 - Eisai - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$ 87.3	$ 107.9
Expense reflected within statements of income	43.6	54.0
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	86.9	5.3
Expense incurred by the collaboration	$ 173.9	$ 10.5