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Investments (Investments Under Equity Method of Accounting) (Parenthetical) (Detail) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Schedule of Equity Method Investments [Line Items] |  |
Liabilities, other deferred credits and other liabilities | $ 17,075 | $ 16,631
NedPower Mount Storm LLC |  |
Schedule of Equity Method Investments [Line Items] |  |
Liabilities, other deferred credits and other liabilities |  | 17
Dominion Energy Gas Holdings, LLC |  |
Schedule of Equity Method Investments [Line Items] |  |
Liabilities, other deferred credits and other liabilities | $ 2,213 | $ 1,901

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