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Fair Value of Financial Instruments - Assets and Liabilities Measured and Recorded at Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | $ 663 | $ 692
Commodity contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 1,042 | 744
Derivative liabilities | 977 | 674
Interest rate contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 39 | 39
Derivative liabilities |  | 6
Cash and cash equivalents |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 19 | 47
U.S. government and federal agency obligations |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 46 | 43
Federal agency mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 100 | 82
Commercial mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 22 | 14
Corporate debt securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 96 | 99
Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 376 | 402
Foreign government fixed income securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 4 | 5
Level 1 | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Equity securities-nuclear trust fund investments | 0 |
Level 2 | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Equity securities-nuclear trust fund investments | 0 |
Level 3 | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Equity securities-nuclear trust fund investments | 0 |
Fair Value, Measurements, Recurring |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Investments in securities (classified within other current or non-current assets) | 39 | 39
U.S. government and federal agency obligations | 1 | 1
Total assets | 1,792 | 1,523
Total liabilities | 977 | 680
Fair Value, Measurements, Recurring | Commodity contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 1,042 | 744
Derivative liabilities | 977 | 674
Fair Value, Measurements, Recurring | Interest rate contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 39 | 39
Derivative liabilities |  | 6
Fair Value, Measurements, Recurring | Cash and cash equivalents |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 19 | 47
Fair Value, Measurements, Recurring | U.S. government and federal agency obligations |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 46 | 43
Fair Value, Measurements, Recurring | Federal agency mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 100 | 82
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 22 | 14
Fair Value, Measurements, Recurring | Corporate debt securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 96 | 99
Fair Value, Measurements, Recurring | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 312 | 334
Equity securities-nuclear trust fund investments | 8 | 8
Fair Value, Measurements, Recurring | Foreign government fixed income securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 4 | 5
Fair Value, Measurements, Recurring | Equity securities-nuclear trust fund investments |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Equity securities-nuclear trust fund investments | 64 | 68
Fair Value, Measurements, Recurring | Level 1 |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Investments in securities (classified within other current or non-current assets) | 2 | 3
U.S. government and federal agency obligations | 1 | 1
Total assets | 517 | 616
Total liabilities | 224 | 257
Fair Value, Measurements, Recurring | Level 1 | Commodity contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 137 | 191
Derivative liabilities | 224 | 257
Fair Value, Measurements, Recurring | Level 1 | Interest rate contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 0 | 0
Derivative liabilities |  | 0
Fair Value, Measurements, Recurring | Level 1 | Cash and cash equivalents |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 19 | 45
Fair Value, Measurements, Recurring | Level 1 | U.S. government and federal agency obligations |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 46 | 42
Fair Value, Measurements, Recurring | Level 1 | Federal agency mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 312 | 334
Fair Value, Measurements, Recurring | Level 1 | Foreign government fixed income securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 2 |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Investments in securities (classified within other current or non-current assets) | 18 | 17
U.S. government and federal agency obligations | 0 | 0
Total assets | 1,075 | 768
Total liabilities | 664 | 364
Fair Value, Measurements, Recurring | Level 2 | Commodity contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 796 | 509
Derivative liabilities | 664 | 358
Fair Value, Measurements, Recurring | Level 2 | Interest rate contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 39 | 39
Derivative liabilities |  | 6
Fair Value, Measurements, Recurring | Level 2 | Cash and cash equivalents |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 2
Fair Value, Measurements, Recurring | Level 2 | U.S. government and federal agency obligations |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 1
Fair Value, Measurements, Recurring | Level 2 | Federal agency mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 100 | 82
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 22 | 14
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 96 | 99
Fair Value, Measurements, Recurring | Level 2 | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 2 | Foreign government fixed income securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 4 | 5
Fair Value, Measurements, Recurring | Level 3 |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Investments in securities (classified within other current or non-current assets) | 19 | 19
U.S. government and federal agency obligations | 0 | 0
Total assets | 128 | 63
Total liabilities | 89 | 59
Fair Value, Measurements, Recurring | Level 3 | Commodity contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 109 | 44
Derivative liabilities | 89 | 59
Fair Value, Measurements, Recurring | Level 3 | Interest rate contracts |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Derivative assets | 0 | 0
Derivative liabilities |  | 0
Fair Value, Measurements, Recurring | Level 3 | Cash and cash equivalents |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | U.S. government and federal agency obligations |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Federal agency mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Equity securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Foreign government fixed income securities |  |
Investment in available-for-sale securities (classified within other non-current assets): |  |
Nuclear trust fund investments | $ 0 | $ 0

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- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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