Nature of Operations (Narrative) (Detail)	12 Months Ended
	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