Collaborative and Other Relationships - Collaborations (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended					12 Months Ended
	Aug. 31, 2021	Jun. 30, 2021	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and Development Expense (Excluding Acquired in Process Cost)			$ 551.7			$ 514.2
Cost of sales, excluding amortization and impairment of acquired intangible assets			753.9			478.1
(Gain) loss on equity method investments			(3.3)			(18.2)
Maximum | Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense								$ 335.0
Samsung Bioepis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
(Gain) loss on equity method investments			4.0			11.0
Loss recorded on Samsung Bioepis joint venture			3.3			18.2
Amortization			7.3			$ 7.2
ADUHELM
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of sales, excluding amortization and impairment of acquired intangible assets			$ 275.0
Eisai
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of future development costs related to Eisai			45.00%			45.00%
Collaboration agreement term			10 years						5 years
Cost of Goods Sold, Capacity Charges			$ 45.0
(Gain) loss on equity method investments			181.7
Due from Related Parties			402.7	$ 285.4					$ 285.4
Due to Related Parties			36.5	46.5					46.5
Eisai | BAN2401 and Elenbecestat
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense Incurred By Collaboration			77.0			$ 55.5
Expense reflected within statements of income			38.5			27.7
Eisai | ADUHELM
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional milestone payment		$ 100.0
(Gain) loss on equity method investments			$ 160.0	59.0	$ 45.0	45.0
Samsung Bioepis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront and milestone payments made to collaborative partner							$ 100.0
Collaboration agreement term			5 years
Research and development expense							$ 63.0
Due from Related Parties			$ 5.8	4.1					4.1
Due to Related Parties			$ 102.5	$ 148.7					148.7
Sangamo Therapeutics, Inc. Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term of collaboration agreement			5 years
Other research and discovery
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and Development Expense (Excluding Acquired in Process Cost)			$ 19.5			1.0
InnoCare Pharma Limited (InnoCare) Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront and milestone payments made to collaborative partner	$ 125.0
Contingent additional milestone payment	$ 812.5
Research and development | Eisai | ADUHELM
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			44.2			47.0
Expense reflected within statements of income			24.3			25.8
Research and development | Denali Therapeutics
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			14.9			15.4
Expense reflected within statements of income			8.9			9.2
Research and development | Samsung Bioepis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			8.3						4.8
Expense reflected within statements of income			5.5						$ 4.2
Research and development | Sage Therapeutics Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			38.7			39.8
Expense reflected within statements of income			19.4			19.9
Research and development | UCB Pharma S.A. [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			17.6			16.9
Expense reflected within statements of income			8.8			8.4
Selling, general and administrative | Eisai | BAN2401 and Elenbecestat
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			15.9			5.7
Expense reflected within statements of income			8.0			2.9
Selling, general and administrative | Eisai | ADUHELM
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			95.0			111.8
Expense reflected within statements of income			50.9			60.3
Selling, general and administrative | Sage Therapeutics Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Expense incurred by the collaboration			18.4			5.3
Expense reflected within statements of income			$ 9.2			$ 2.7