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Nature of Operations (Narrative) (Detail)
12 Months Ended
Dec. 31, 2018
Segments
Subsidiary, Sale of Stock [Line Items]  
Number of operating segments 3
Iroquois  
Subsidiary, Sale of Stock [Line Items]  
Ownership percentage 50.00% [1]
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
Dominion Energy Gas Holdings, LLC | Iroquois  
Subsidiary, Sale of Stock [Line Items]  
Ownership percentage 50.00%
Dominion Energy Gas Holdings, LLC | White River Hub  
Subsidiary, Sale of Stock [Line Items]  
Ownership percentage 50.00%
[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.