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Financial Instruments Financial Instruments (Details Textual 2) - USD ($) $ / shares in Units, shares in Millions, number in Millions, $ in Millions	1 Months Ended			3 Months Ended
	Nov. 30, 2020	Apr. 30, 2020	Feb. 29, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Proceeds from sales of strategic investments				$ 91.2	$ 0.5
Sage Therapeutics Inc.
Business Acquisition [Line Items]
Global Licensing Collaboration Agreement, Amount, Shares Purchased	$ 650.0
Global Licensing Collaboration Agreement, Shares, Purchased	6.2
Global Licensing Collaboration Agreement, Purchase Price Per Share	$ 104.14
Dividend yield percentage				0.00%
Sangamo Therapeutics, Inc. Agreement
Business Acquisition [Line Items]
Global Licensing Collaboration Agreement, Amount, Shares Purchased			$ 225.0
Global Licensing Collaboration Agreement, Shares, Purchased			24.0
Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio				$ 1,493.1
Other noncurrent assets | Strategic Investments
Business Acquisition [Line Items]
Strategic investment portfolio						$ 2,024.6
Denali Therapeutics
Business Acquisition [Line Items]
Investment in common stock, shares purchased				13.0
Dividend yield percentage				0.00%
Sangamo
Business Acquisition [Line Items]
Dividend yield percentage		0.00%

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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