Collaborative and Other Relationships - Summary of Activity Related to ADUHELM Collaboration (Details) - Eisai - ADUHELM $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Research and development
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	$ 44.2
Expense reflected within statements of income	24.3
Selling, general and administrative
Collaborative arrangements and non-collaborative arrangement transactions
Expense incurred by the collaboration	95.0
Expense reflected within statements of income	$ 50.9