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Fair Value of Financial Instruments - Assets and Liabilities Measured and Recorded at Fair Value (Details) - USD ($) $ in Millions | Mar. 31, 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) | $ 24 | $ 25
Other trust fund investments: |  |
U.S. government and federal agency obligations | 1 | 1
Measured using net asset value practical expedient: |  |
Total assets | 3,766 | 1,745
Derivative liabilities: |  |
Commodity contracts | 2,440 | 884
Commodity contracts |  |
Derivative assets: |  |
Commodity contracts | 2,824 | 821
Derivative liabilities: |  |
Commodity contracts | 2,438 | 884
Foreign exchange contract |  |
Derivative liabilities: |  |
Commodity contracts | 2 |
Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 20 | 23
U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 73 | 70
Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 78 | 89
Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 40 | 36
Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 136 | 144
Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 466 | 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 | 7 | 7
Equity securities — nuclear trust fund investments |  |
Measured using net asset value practical expedient: |  |
Equity securities | 89 | 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) | 10 | 10
Other trust fund investments: |  |
U.S. government and federal agency obligations | 1 | 1
Measured using net asset value practical expedient: |  |
Total assets | 765 | 597
Derivative liabilities: |  |
Commodity contracts | 205 | 86
Level 1 | Commodity contracts |  |
Derivative assets: |  |
Commodity contracts | 195 | 59
Derivative liabilities: |  |
Commodity contracts | 205 | 86
Level 1 | Foreign exchange contract |  |
Derivative liabilities: |  |
Commodity contracts | 0 |
Level 1 | Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 20 | 23
Level 1 | U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 72 | 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 | 466 | 434
Level 1 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 1 | 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) | 14 | 15
Other trust fund investments: |  |
U.S. government and federal agency obligations | 0 | 0
Measured using net asset value practical expedient: |  |
Total assets | 2,640 | 914
Derivative liabilities: |  |
Commodity contracts | 2,130 | 643
Level 2 | Commodity contracts |  |
Derivative assets: |  |
Commodity contracts | 2,365 | 623
Derivative liabilities: |  |
Commodity contracts | 2,128 | 643
Level 2 | Foreign exchange contract |  |
Derivative liabilities: |  |
Commodity contracts | 2 |
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 | 78 | 89
Level 2 | Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 40 | 36
Level 2 | Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 136 | 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 | 6 | 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: |  |
U.S. government and federal agency obligations | 0 | 0
Measured using net asset value practical expedient: |  |
Total assets | 264 | 139
Derivative liabilities: |  |
Commodity contracts | 105 | 155
Level 3 | Commodity contracts |  |
Derivative assets: |  |
Commodity contracts | 264 | 139
Derivative liabilities: |  |
Commodity contracts | 105 | 155
Level 3 | Foreign exchange contract |  |
Derivative liabilities: |  |
Commodity contracts | 0 |
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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