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Fair Value of Financial Instruments - Assets and Liabilities Measured and Recorded at Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in securities (classified within other current and non-current assets) | $ 20 | $ 39
Other trust fund investments: |  |
Other trust fund investments | 1 | 1
Measured using net asset value practical expedient: |  |
Total assets | 1,993 | 1,792
Derivative liabilities: |  |
Total liabilities | 1,103 | 977
Commodity contracts |  |
Derivative assets: |  |
Derivative assets | 1,170 | 1,042
Derivative liabilities: |  |
Commodity contracts | 1,103 | 977
Interest rate contracts |  |
Derivative assets: |  |
Derivative assets |  | 39
Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 17 | 19
U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 68 | 46
Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 100 | 100
Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 29 | 22
Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 109 | 96
Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 388 | 312
Measured using net asset value practical expedient: |  |
Equity contracts | 8 | 8
Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 5 | 4
Equity securities-nuclear trust fund investments |  |
Measured using net asset value practical expedient: |  |
Equity contracts | 78 | 64
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) | 0 | 2
Other trust fund investments: |  |
Other trust fund investments | 1 | 1
Measured using net asset value practical expedient: |  |
Total assets | 558 | 517
Derivative liabilities: |  |
Total liabilities | 143 | 224
Level 1 | Commodity contracts |  |
Derivative assets: |  |
Derivative assets | 84 | 137
Derivative liabilities: |  |
Commodity contracts | 143 | 224
Level 1 | Interest rate contracts |  |
Derivative assets: |  |
Derivative assets |  | 0
Level 1 | Cash and cash equivalents |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 17 | 19
Level 1 | U.S. government and federal agency obligations |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 68 | 46
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 | 388 | 312
Measured using net asset value practical expedient: |  |
Equity contracts | 0 | 0
Level 1 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 1 | Equity securities-nuclear trust fund investments |  |
Measured using net asset value practical expedient: |  |
Equity contracts | 0 | 0
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) | 20 | 18
Other trust fund investments: |  |
Other trust fund investments | 0 | 0
Measured using net asset value practical expedient: |  |
Total assets | 1,156 | 1,075
Derivative liabilities: |  |
Total liabilities | 805 | 664
Level 2 | Commodity contracts |  |
Derivative assets: |  |
Derivative assets | 893 | 796
Derivative liabilities: |  |
Commodity contracts | 805 | 664
Level 2 | Interest rate contracts |  |
Derivative assets: |  |
Derivative assets |  | 39
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 | 0 | 0
Level 2 | Federal agency mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 100 | 100
Level 2 | Commercial mortgage-backed securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 29 | 22
Level 2 | Corporate debt securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 109 | 96
Level 2 | Equity securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Measured using net asset value practical expedient: |  |
Equity contracts | 0 | 0
Level 2 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 5 | 4
Level 2 | Equity securities-nuclear trust fund investments |  |
Measured using net asset value practical expedient: |  |
Equity contracts | 0 | 0
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 | 19
Other trust fund investments: |  |
Other trust fund investments | 0 | 0
Measured using net asset value practical expedient: |  |
Total assets | 193 | 128
Derivative liabilities: |  |
Total liabilities | 155 | 89
Level 3 | Commodity contracts |  |
Derivative assets: |  |
Derivative assets | 193 | 109
Derivative liabilities: |  |
Commodity contracts | 155 | 89
Level 3 | Interest rate contracts |  |
Derivative assets: |  |
Derivative assets |  | 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
Measured using net asset value practical expedient: |  |
Equity contracts | 0 | 0
Level 3 | Foreign government fixed income securities |  |
Nuclear trust fund investments: |  |
Nuclear trust fund investments | 0 | 0
Level 3 | Equity securities-nuclear trust fund investments |  |
Measured using net asset value practical expedient: |  |
Equity contracts | $ 0 | $ 0

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