Maximum shares the collaborator could sell through September 30, 2020.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

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No definition available.

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Amount of stock repurchase plan authorized.

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Amount remaining of a stock repurchase plan authorized.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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Stockholders' Equity - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended					9 Months Ended
Stockholders' Equity - Narrative (Details) - USD ($)	May 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Nov. 30, 2019
Class of Stock [Line Items]
Treasury stock, shares acquired (in shares)	9,806,805
Cost of treasury stock received	$ 5,000,000,000	$ 100,400,000	$ 5,071,800,000	$ 336,000,000.0	$ 48,700,000	$ 54,000,000.0
Sanofi Collaboration Agreement, Immuno-oncology
Class of Stock [Line Items]
Maximum shares the collaborator could sell (in shares)		279,766					279,766
Sanofi
Class of Stock [Line Items]
Number of shares sold (in shares)	13,014,646
Common Stock, shares outstanding (in shares)	400,000
Share Repurchase Program
Class of Stock [Line Items]
Share repurchase program, authorized amount								$ 1,000,000,000.0
Remaining authorized repurchase amount		$ 372,700,000					$ 372,700,000
Treasury stock, shares acquired (in shares)		179,824					898,991
Cost of treasury stock received		$ 100,400,000					$ 373,300,000