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Investments in Unconsolidated Affiliates (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Sep. 06, 2019 | Sep. 05, 2019 | Dec. 31, 2016
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Distributions from equity investments | $ 55 | $ 108 | $ 13 |  |  |
Distributions from equity investments, return of capital | $ 11 | 137 | $ 281 |  |  |
Constitution | VIE, Not Primary Beneficiary |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest | 24.00% |  |  |  |  |
ACP |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Distributions from equity investments, return of capital | $ 265 |  |  |  |  |
Electric Utilities and Infrastructure | DATC |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest | 50.00% |  |  |  |  |
Electric Utilities and Infrastructure | Pioneer |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest | 50.00% |  |  |  |  |
Commercial Renewables | DS Cornerstone |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest |  |  |  | 26.00% | 50.00% |
Gas Utilities and Infrastructure | Constitution | VIE, Not Primary Beneficiary |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
OTTI impairment loss | $ 25 | 55 |  |  |  |
Gas Utilities and Infrastructure | ACP |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest | 47.00% |  |  |  |  |
Gas Utilities and Infrastructure | Constitution |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest | 24.00% |  |  |  |  |
Gas Utilities and Infrastructure | Constitution | Constitution | VIE, Not Primary Beneficiary |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
OTTI impairment loss | $ 25 |  |  |  |  |
Other | NMC |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Ownership interest | 17.50% |  | 17.50% |  |  | 25.00%
Board representation and voting rights, ownership percentage | 25.00% |  |  |  |  |
Piedmont |  |  |  |  |  |
Investments In Unconsolidated Affiliates [Line Items] |  |  |  |  |  |
Distributions from equity investments | $ 1 | 1 | $ 4 |  |  |
Distributions from equity investments, return of capital | $ 4 | $ 3 | $ 2 |  |  |

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