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Investments in Unconsolidated Affiliates (Gas Utilities and Infrastructure Investments) (Details) - USD ($) $ in Millions | 2 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Oct. 31, 2016
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Investments in equity method unconsolidated affiliates | $ 925 | $ 1,409 | $ 1,175 | $ 925 |
Return of investment capital |  | 137 | 281 | 1 |
Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Investments in equity method unconsolidated affiliates | 566 | 1,003 | 763 | $ 566 |
Atlantic Coast Pipeline [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Return of investment capital |  | $ 265 |  |  |
Atlantic Coast Pipeline [Member] | Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 47.00% |  |  |
Investments in equity method unconsolidated affiliates |  | $ 797 | 397 |  |
Sabal Trail Transmission Pipeline [Member] | Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 7.50% |  |  |
Investments in equity method unconsolidated affiliates |  | $ 112 | 219 |  |
Return of investment capital |  | $ 112 |  |  |
Constitution Pipeline [Member] | Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 24.00% |  |  |
Investments in equity method unconsolidated affiliates |  | $ 25 | 81 |  |
Piedmont Natural Gas [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Investments in equity method unconsolidated affiliates |  | 64 | 61 |  |
Return of investment capital | $ 1 | $ 3 | 2 |  | $ 18
Piedmont Natural Gas [Member] | Cardinal Pipeline Company, LLC [Member] | Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 21.49% |  |  |
Investments in equity method unconsolidated affiliates |  | $ 10 | 11 |  |
Piedmont Natural Gas [Member] | Pine Needle LNG Company, LLC [Member] | Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 45.00% |  |  |
Investments in equity method unconsolidated affiliates |  | $ 13 | 13 |  |
Piedmont Natural Gas [Member] | Hardy Storage Company, LLC [Member] | Gas Utilities and Infrastructure [Member] |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 50.00% |  |  |
Investments in equity method unconsolidated affiliates |  | $ 46 | $ 42 |  |

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