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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
Iroquois |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Ownership% | [1] | 50.00% |
NedPower Mount Storm LLC |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Liabilities, other deferred credits and other liabilities |  | $ 1 | 17
Dominion Energy Midstream Partners, LP | Iroquois |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Ownership% |  | 25.93% |
Dominion Energy Gas Holdings, LLC |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Liabilities, other deferred credits and other liabilities |  | $ 2,944 | $ 2,866
Dominion Energy Gas Holdings, LLC | Iroquois |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Ownership% |  | 24.07% |
[1] | Comprised of Dominion Energy Midstream's interest of 25.93% and Dominion Energy Gas' interest of 24.07%. See Note 15 for more information.

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