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Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2020 | Dec. 31, 2019
Fair Value of Financial Instruments [Line Items] |  |
Noncurrent liabilities - held for sale (Note 10) | $ 718 | $ 691
Investments - held for sale (Note 10) | 881 | 882
Investments not required to be disclosed | $ 301 | $ 299
NUG contracts |  |
Fair Value of Financial Instruments [Line Items] |  |
Period of future observable data to determine contract price | 2 years |

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