Financial Instruments - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions, ₩ in Billions	1 Months Ended					12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) $ / shares shares	Nov. 30, 2018 USD ($)	Nov. 30, 2018 KRW (₩)	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2021 KRW (₩) shares	Dec. 31, 2020 KRW (₩)	Jun. 30, 2018	May 31, 2018	Feb. 29, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Business Acquisition [Line Items]
Average maturity of marketable securities, months						10 months	11 months
Sage Therapeutics
Business Acquisition [Line Items]
Global licensing collaboration, shares purchased, amount | $	$ 650.0
Global licensing collaboration, shares purchased (in shares) | shares	6.2
Global licensing collaboration, purchase price per share (in dollars per share) | $ / shares	$ 104.14
Denali Therapeutics
Business Acquisition [Line Items]
Global licensing collaboration, shares purchased, amount | $		$ 465.0
Global licensing collaboration, shares purchased (in shares) | shares		13.0
Global licensing collaboration, purchase price per share (in dollars per share) | $ / shares		$ 34.94
Sangamo Therapeutics, Inc. Agreement
Business Acquisition [Line Items]
Global licensing collaboration, shares purchased, amount | $			$ 225.0
Global licensing collaboration, shares purchased (in shares) | shares			24.0
Global licensing collaboration, purchase price per share (in dollars per share) | $ / shares			$ 9.21
Investment in common stock, shares purchased (in shares) | shares						12.0		12.0
Samsung Bioepis
Business Acquisition [Line Items]
Ownership percentage before additional purchase transaction											5.00%
Ownership percentage						49.90%		49.90%		49.90%		15.00%	15.00%
Payments to increase investment in Samsung Bioepis				$ 676.6	₩ 759.5
Investment in Samsung Bioepis	$ 620.2					$ 599.9	$ 620.2	₩ 713.3	₩ 673.8			$ 45.0	₩ 49.5
Sage Therapeutics
Business Acquisition [Line Items]
Dividend yield percentage						0.00%
Denali Therapeutics
Business Acquisition [Line Items]
Dividend yield percentage						0.00%
Sangamo Therapeutics
Business Acquisition [Line Items]
Dividend yield percentage						0.00%
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio | $	$ 2,024.6					$ 1,110.3	$ 2,024.6