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Financial Instruments - Summarized Information About Changes in Liabilities for Contingent Consideration (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Contingent consideration | $ 767 | $ 788
Additions | 97 | 0
Changes in estimated fair value | 83 | 64
Payments | (106) | (85)
Contingent consideration | 841 | 767
Contingent consideration, liability, current | $ 148 |
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 | $ 625 |
Contingent consideration | $ 711 | $ 625
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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