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Fair Value of Financial Instruments - Assets and Liabilities Measured and Recorded at Fair Value (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in securities (classified within other current and non-current assets) | $ 23 | $ 25
Other trust fund investments (classified within other non-current assets): |  |
U.S. government and federal agency obligations | 1 | 1
Measured using net asset value practical expedient: |  |
Total assets | 12,188 | 1,745
Derivative liabilities: |  |
Commodity contracts | 7,521 | 884
Foreign exchange contract |  |
Derivative assets: |  |
Derivative contracts | 1 |
Commodity contracts |  |
Derivative assets: |  |
Derivative contracts | 11,198 | 821
Derivative liabilities: |  |
Commodity contracts | 7,521 | 884
Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 29 | 23
U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 76 | 70
Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 93 | 89
Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 43 | 36
Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 116 | 144
Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 503 | 434
Measured using net asset value practical expedient: |  |
Equity securities | 8 | 8
Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 4 | 7
Equity securities — nuclear trust fund investments |  |
Measured using net asset value practical expedient: |  |
Equity securities | 93 | 87
Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in securities (classified within other current and non-current assets) | 7 | 10
Other trust fund investments (classified within other non-current assets): |  |
U.S. government and federal agency obligations | 1 | 1
Measured using net asset value practical expedient: |  |
Total assets | 2,776 | 597
Derivative liabilities: |  |
Commodity contracts | 1,376 | 86
Level 1 | Foreign exchange contract |  |
Derivative assets: |  |
Derivative contracts | 0 |
Level 1 | Commodity contracts |  |
Derivative assets: |  |
Derivative contracts | 2,161 | 59
Derivative liabilities: |  |
Commodity contracts | 1,376 | 86
Level 1 | Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 29 | 23
Level 1 | U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 75 | 69
Level 1 | Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 1 | Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 1 | Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 1 | Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 503 | 434
Level 1 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 1
Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in securities (classified within other current and non-current assets) | 16 | 15
Other trust fund investments (classified within other non-current assets): |  |
U.S. government and federal agency obligations | 0 | 0
Measured using net asset value practical expedient: |  |
Total assets | 8,748 | 914
Derivative liabilities: |  |
Commodity contracts | 5,893 | 643
Level 2 | Foreign exchange contract |  |
Derivative assets: |  |
Derivative contracts | 1 |
Level 2 | Commodity contracts |  |
Derivative assets: |  |
Derivative contracts | 8,474 | 623
Derivative liabilities: |  |
Commodity contracts | 5,893 | 643
Level 2 | Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 2 | U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 1 | 1
Level 2 | Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 93 | 89
Level 2 | Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 43 | 36
Level 2 | Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 116 | 144
Level 2 | Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 2 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 4 | 6
Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in securities (classified within other current and non-current assets) | 0 | 0
Other trust fund investments (classified within other non-current assets): |  |
U.S. government and federal agency obligations | 0 | 0
Measured using net asset value practical expedient: |  |
Total assets | 563 | 139
Derivative liabilities: |  |
Commodity contracts | 252 | 155
Level 3 | Foreign exchange contract |  |
Derivative assets: |  |
Derivative contracts | 0 |
Level 3 | Commodity contracts |  |
Derivative assets: |  |
Derivative contracts | 563 | 139
Derivative liabilities: |  |
Commodity contracts | 252 | 155
Level 3 | Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | $ 0 | $ 0

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