Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) segment	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Property, Plant and Equipment [Line Items]
Interest in subsidiary (less than given percentage)	100.00%
Number of operating segments	1
Number of reportable segment	1
Advertising costs | $	$ 71.9	$ 66.8	$ 71.4
LEQEMBI Collaboration
Property, Plant and Equipment [Line Items]
Share of non-controling interest recognized	50.00%
Minimum
Property, Plant and Equipment [Line Items]
Payment terms of accounts receivable arising from product sales	30 days
Minimum | Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Payment terms of accounts receivable arising from product sales	90 days
Maximum | Computer Software and Hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years