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Financial Instruments - Information About Changes in Liabilities for Contingent Consideration (Details) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 841	$ 767	$ 767
Additions	0	97
Changes in estimated fair value	50	40
Payments	0	(106)
Other	(12)	0
Fair value, ending balance	879	798	841
Current liability	297
Contingent consideration	879	$ 798	841
Sanofi Pasteur
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	711
Fair value, ending balance	759		711
Contingent consideration	$ 759		$ 711
Contingent consideration, measurement input, discount rate (as percent)	0.115
Measurement Input, Discount Rate | Sanofi Pasteur
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration, measurement input, discount rate (as percent)	0.08

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Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

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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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Value of input used to measure contingent consideration liability from business combination.

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Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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