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Quarterly Financial and Common Stock Data (Unaudited) (Narrative) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2017
Parent Company Only Financial Information [Line Items] |  |  |
Tax benefit resulting from remeasurement of deferred income taxes as a result of the 2017 Tax Reform Act | $ (851) |  | $ (851)
Charges associated with equity method investments in wind-powered generation facilities, after tax | 96 |  |
Virginia Electric and Power Company |  |  |
Parent Company Only Financial Information [Line Items] |  |  |
Tax benefit resulting from remeasurement of deferred income taxes as a result of the 2017 Tax Reform Act | (93) |  | (93)
Dominion Energy Gas Holdings, LLC |  |  |
Parent Company Only Financial Information [Line Items] |  |  |
Tax benefit resulting from remeasurement of deferred income taxes as a result of the 2017 Tax Reform Act | $ (197) |  | $ (197)
Facilities Subject to Coal Combustion Residual Final Rule |  |  |
Parent Company Only Financial Information [Line Items] |  |  |
Charge related to future ash pond and landfill closure costs |  | $ 122 |
Facilities Subject to Coal Combustion Residual Final Rule | Virginia Electric and Power Company |  |  |
Parent Company Only Financial Information [Line Items] |  |  |
Charge related to future ash pond and landfill closure costs |  | $ 121 |

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