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Financial Instruments - Summarized Information About Changes in Liabilities for Contingent Consideration (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	$ 788	$ 935
Changes in estimated fair value	64	89
Additions	0	8
Payments	(85)	(244)
Contingent consideration	767	788
Contingent consideration, liability, current	$ 114
Sanofi Pasteur
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	0.115
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration	$ 614
Contingent consideration	$ 625	$ 614
Measurement Input, Discount Rate | Sanofi Pasteur
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	0.08

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Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

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Amount of liability recognized arising from contingent consideration in a business combination.

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