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Strategic investment portfolio.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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Financial Instruments - Narrative (Details) shares in Millions, $ in Millions, ₩ in Billions	1 Months Ended		12 Months Ended
	Nov. 30, 2018 USD ($)	Nov. 30, 2018 KRW (₩)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 KRW (₩)	Nov. 30, 2020 shares	Sep. 30, 2020 shares	Apr. 30, 2020 shares	Dec. 31, 2019 KRW (₩)	Jun. 30, 2018	Feb. 29, 2012 USD ($)	Feb. 29, 2012 KRW (₩)
Business Acquisition [Line Items]
Average maturity of marketable securities, months			11 months	14 months
Payments to increase investment in Samsung Bioepis \| $			$ 0.0	$ 0.0	$ 676.6
Sage Therapeutics
Business Acquisition [Line Items]
Dividend yield percentage			0.00%
Sage Therapeutics \| Significant Other Observable Inputs (Level 2)
Business Acquisition [Line Items]
Investment in common stock, shares purchased (in shares)							6.2
Denali Therapeutics
Business Acquisition [Line Items]
Dividend yield percentage			0.00%
Denali Therapeutics \| Significant Other Observable Inputs (Level 2)
Business Acquisition [Line Items]
Investment in common stock, shares purchased (in shares)								13.0
Sangamo Therapeutics
Business Acquisition [Line Items]
Investment in common stock, shares purchased (in shares)									24.0
Dividend yield percentage			0.00%
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio \| $			$ 2,024.6	393.9
Samsung Bioepis
Business Acquisition [Line Items]
Samsung Bioepis, ownership percentage before additional purchase transaction											5.00%
Samsung Bioepis, ownership percentage			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	$ 580.2		₩ 673.8				₩ 670.8		$ 45.0	₩ 49.5