Operating Segments (Narrative) (Detail) - Operating Segments - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
After- tax net (expenses) benefit	$ (218)
Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net (expenses) benefit	(189)
Storm damage and service restoration costs associated with winter storm riley	31
Storm damage and service restoration costs associated with winter storm riley, after tax	23
Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with legislation enacted	215
Charge associated with legislation enacted, after tax	160
Virginia Regulation | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Charge associated with legislation enacted	215
Charge associated with legislation enacted, after tax	160
Decommissioning Trust Fund
Segment Reporting Information [Line Items]
Loss on investments held in nuclear decommissioning trust funds	43
Loss on investments held in nuclear decommissioning trust funds, after tax	32
Net gain on investments held in nuclear decommissioning trust funds			$ 34
Net gain on investments held in nuclear decommissioning trust funds, after tax			$ 21
Corporate and Other
Segment Reporting Information [Line Items]
After- tax net (expenses) benefit	(238)	$ 21
Corporate and Other | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net (expenses) benefit	(197)	2
Corporate and Other | Dominion Energy Gas Holdings, LLC
Segment Reporting Information [Line Items]
After- tax net (expenses) benefit	0	$ 0
Power Generation | Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	109
Power Generation | Virginia Regulation | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	109
Power Delivery | Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	51
Power Delivery | Virginia Regulation | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	$ 51