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Nature of Operations (Narrative) (Detail) | 12 Months Ended
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Dec. 31, 2018 Segments
Subsidiary, Sale of Stock [Line Items] |
Number of operating segments | 3
Iroquois | Partnership Interest | Dominion Energy Midstream Partners, LP |
Subsidiary, Sale of Stock [Line Items] |
Noncontrolling partnership percentage interest | 25.93%
Common and Subordinated Units | Dominion Energy Midstream Partners, LP |
Subsidiary, Sale of Stock [Line Items] |
Ownership interest percentage of limited partner interests | 60.90%
Convertible Preferred Units | Dominion Energy Midstream Partners, LP |
Subsidiary, Sale of Stock [Line Items] |
Ownership interest percentage of limited partner interests | 37.50%
Virginia Electric and Power Company |
Subsidiary, Sale of Stock [Line Items] |
Number of operating segments | 2
Dominion Energy Gas Holdings, LLC |
Subsidiary, Sale of Stock [Line Items] |
Number of operating segments | 1

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