Collaborative and Other Relationships - Summary of Activity Related to ADUHELM Collaboration (Details) - Eisai - ADUHELM - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2022
Research and development
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 37.2	$ 81.4
Expense reflected within statements of income	20.5	44.8
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	40.8	135.8
Expense reflected within statements of income	$ 21.1	$ 72.0