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Variable Interest Entities (Narrative) (Detail) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) MW Generators | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) Generators
Variable Interest Entity [Line Items] |  |  |
Securities due within one year | $ 3,078 | $ 1,709 |
Long term debt | 30,948 | 30,231 |
Virginia Electric and Power Company |  |  |
Variable Interest Entity [Line Items] |  |  |
Securities due within one year | 850 | 678 |
Long term debt | 10,496 | 9,852 |
Dominion Energy Gas Holdings, LLC |  |  |
Variable Interest Entity [Line Items] |  |  |
Long term debt | $ 3,570 | 3,528 |
Variable Interest Entity, Primary Beneficiary | Partnership Interest | Merchant Solar Projects |  |  |
Variable Interest Entity [Line Items] |  |  |
Initial membership interest percentage | 67.00% |  |
Variable Interest Entity, Primary Beneficiary | SBL Holdco |  |  |
Variable Interest Entity [Line Items] |  |  |
Securities due within one year | $ 30 |  |
Long term debt | $ 332 |  |
Variable Interest Entity, Primary Beneficiary | Dominion Energy Midstream Partners, LP | Partnership Interest | Limited Partner |  |  |
Variable Interest Entity [Line Items] |  |  |
Percentage of limited partner interests in Dominion Midstream Partners, LP | 50.60% |  |
Variable Interest Entity, Primary Beneficiary | Dominion Energy Midstream Partners, LP | Partnership Interest | Preferred Partner |  |  |
Variable Interest Entity [Line Items] |  |  |
Percentage of limited partner interests in Dominion Midstream Partners, LP | 37.50% |  |
Variable Interest Entity, Not Primary Beneficiary | Distribution | Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline |  |  |
Variable Interest Entity [Line Items] |  |  |
Initial membership interest percentage | 48.00% |  |
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES |  |  |
Variable Interest Entity [Line Items] |  |  |
Shared services purchased | $ 340 | 346 | $ 318
Variable Interest Entity, Not Primary Beneficiary | Dominion Energy Gas Holdings, LLC | DES |  |  |
Variable Interest Entity [Line Items] |  |  |
Shared services purchased | $ 126 | 123 | $ 115
Variable Interest Entity (VIE) or Potential VIE, Information Unavailability | Virginia Electric and Power Company |  |  |
Variable Interest Entity [Line Items] |  |  |
Long term capacity contract non utility generators (generators) | Generators |  |  | 5
Number of expired non-utility generators | Generators |  |  | 2
Number of expired additional non-utility generators | Generators | 2 |  |
Aggregate generation capacity from long-term power and capacity contracts (MW) | MW | 218 |  |
Remaining purchase commitments | $ 200 |  |
Payment for electric capacity | 86 | 144 | $ 200
Payment for electric energy | $ 24 | $ 31 | $ 83

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