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Investments in Unconsolidated Affiliates (Gas Utilities and Infrastructure Investments) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Investments in equity method unconsolidated affiliates | $ 1,936 | $ 1,409 | $ 1,175
Return of investment capital | 11 | 137 | 281
ACP |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Return of investment capital | 265 |  |
Gas Utilities and Infrastructure |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Investments in equity method unconsolidated affiliates | $ 1,388 | 1,003 | 763
Gas Utilities and Infrastructure | ACP |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Ownership interest | 47.00% |  |
Investments in equity method unconsolidated affiliates | $ 1,179 | 797 |
Gas Utilities and Infrastructure | Sabal Trail |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Ownership interest | 7.50% |  |
Investments in equity method unconsolidated affiliates | $ 121 | 112 |
Return of investment capital |  | 112 |
Gas Utilities and Infrastructure | Constitution |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Ownership interest | 24.00% |  |
Investments in equity method unconsolidated affiliates |  | 25 |
Piedmont |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Investments in equity method unconsolidated affiliates | $ 83 | 64 |
Return of investment capital | $ 4 | 3 | $ 2
Piedmont | Gas Utilities and Infrastructure | Cardinal |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Ownership interest | 21.49% |  |
Investments in equity method unconsolidated affiliates | $ 9 | 10 |
Piedmont | Gas Utilities and Infrastructure | Pine Needle |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Ownership interest | 45.00% |  |
Investments in equity method unconsolidated affiliates | $ 28 | 13 |
Piedmont | Gas Utilities and Infrastructure | Hardy Storage |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |
Ownership interest | 50.00% |  |
Investments in equity method unconsolidated affiliates | $ 51 | $ 46 |

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