Collaborative and Other Relationships - Equity Method Investments (Details) $ in Millions, ₩ in Billions	1 Months Ended	3 Months Ended
	Jan. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2022 KRW (₩)	Dec. 31, 2021 KRW (₩)	Jan. 31, 2020 USD ($)	Nov. 07, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments		$ (3.3)			$ (18.2)
Collaboration profit (loss) sharing		$ (117.3)			68.5
Samsung Bioepis
Schedule of Equity Method Investments [Line Items]
Percentage of stake in entity maximum		49.90%					49.90%
Amortization of basis differences										$ 675.0
Loss recorded on Samsung Bioepis joint venture		$ 3.3			18.2
Income (loss) from equity method investments		4.0			11.0
Investment in Samsung Bioepis		586.4	$ 599.9				₩ 709.4	₩ 713.3
Collaboration profit (loss) sharing		64.4			68.5
Eisai
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments		181.7
Due to Related Parties		36.5	46.5
Eisai | ADUHELM
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments		$ 160.0	59.0	$ 45.0	$ 45.0
Samsung Bioepis
Schedule of Equity Method Investments [Line Items]
Proceeds from Divestiture of Interest in Joint Venture	$ 1,000.0
Payables To Divestiture Of Interest In Joint Venture	1,300.0
Equity Method Investments, Expected Profit Share		50.00%
Upfront and milestone payments made to collaborative partner						$ 100.0
Research and development expense						$ 63.0
Prepaid research and development expenses									$ 37.0
Accrued milestone payments		$ 15.0
Estimated additional payments upon achievement of development and commercial milestones	50.0	180.0
Contract Option Exercise Fee		60.0
Due to Related Parties		$ 102.5	$ 148.7
Samsung Bioepis | Payment Due At First Anniversary
Schedule of Equity Method Investments [Line Items]
Payables To Divestiture Of Interest In Joint Venture	812.5
Samsung Bioepis | Payment Due At Second Anniversary
Schedule of Equity Method Investments [Line Items]
Payables To Divestiture Of Interest In Joint Venture	$ 437.5
Inventory | Samsung Bioepis
Schedule of Equity Method Investments [Line Items]
Equity method investment basis difference amortization period		1 year 6 months
Developed technology | Samsung Bioepis
Schedule of Equity Method Investments [Line Items]
Equity method investment basis difference amortization period		15 years