Collaborative and Other Relationships - Summary of Activity Related to BAN2401 and Elenbecestat Collaboration (Details) - Eisai - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative arrangements and non-collaborative arrangement transactions
Total development expense incurred by the collaboration related to the advancement of lecanemab and elenbecestat	$ 323.0	$ 219.3	$ 348.7
Expense reflected within statements of income	161.5	109.6	174.3
Selling, general and administrative | E2609 and BAN2401
Collaborative arrangements and non-collaborative arrangement transactions
Expense reflected within statements of income	13.6	4.9	16.2
Expense incurred by the collaboration	$ 27.2	$ 9.8	$ 32.4