Collaborative and Other Relationships - Eisai (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Jul. 31, 2023	Mar. 31, 2023
LEQEMBI Collaboration
Collaborative arrangements and non-collaborative arrangement transactions
Share of non-controling interest recognized	50.00%	50.00%
Eisai
Collaborative arrangements and non-collaborative arrangement transactions
Accrued payment to termination agreement			$ 31.0
Payments made to termination agreement	$ 16.0
Related cost-sharing reduction (as a percentage)	80.00%
Eisai | LEQEMBI Collaboration | Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Term of collaboration agreement	5 years
Eisai | LEQEMBI Collaboration | Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Term of collaboration agreement	10 years