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Other Consolidated Financial Statement - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Collaborative arrangements and non-collaborative arrangement transactions
Net unrealized (gains) losses recognized on equity securities	$ 25.1	$ (3.2)	$ (36.8)	$ 32.5
Prepaid Taxes	943.7		943.7		$ 693.6
Other liabilities, noncurrent	668.4		668.4		748.5
Accrued income taxes	179.1		179.1		$ 166.4
Sage and Denali
Collaborative arrangements and non-collaborative arrangement transactions
Net unrealized (gains) losses recognized on equity securities		$ 3.8
Denali Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Net unrealized (gains) losses recognized on equity securities	$ 23.7		$ 42.2	41.9
Sage Therapeutics
Collaborative arrangements and non-collaborative arrangement transactions
Net unrealized (gains) losses recognized on equity securities				$ 23.0