Operating Segments (Narrative) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
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
Operating Segments
Segment Reporting Information [Line Items]
After- tax net expenses	(188)	$ (1)
Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net expenses	(226)
Operating Segments | Dominion Energy Gas Holdings, LLC
Segment Reporting Information [Line Items]
After- tax net expenses	(99)
Disallowance charge	124
Disallowance charge, after tax	88
Write off of regulatory asset		15
Write off of regulatory asset, after tax		9
Operating Segments | Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with legislation enacted	215
Charge associated with legislation enacted, after tax	160
Operating Segments | 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
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
After- tax net expenses	(253)	(17)
Corporate and Other | Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net expenses	(229)	(7)
Corporate and Other | Operating Segments | Dominion Energy Gas Holdings, LLC
Segment Reporting Information [Line Items]
After- tax net expenses	(100)	(9)
Power Generation | Operating Segments | Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	109
Power Generation | Operating Segments | Virginia Regulation | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	109
Power Generation | Operating Segments | Nuclear Decommissioning Trust Funds
Segment Reporting Information [Line Items]
Net investment earnings on nuclear decommissioning trust funds	156
Net investment earnings on nuclear decommissioning trust funds, after tax	121
Power Generation | Operating Segments | Virginia Legislation | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Asset retirement obligations	81
Asset retirement obligations, after tax	60
Power Generation | Operating Segments | Ash Ponds and Landfills Certain Utility Generation Facility | Virginia Legislation
Segment Reporting Information [Line Items]
Asset retirement obligations	81
Asset retirement obligations, after tax	60
Power Delivery | Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Customer settlement		16
Customer settlement, after tax		$ 10
Power Delivery | Operating Segments | Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	51
Power Delivery | Operating Segments | Virginia Regulation | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Charge associated with legislation enacted, after tax	51
Gas Infrastructure | Operating Segments | Federal Energy Regulatory Commission
Segment Reporting Information [Line Items]
Disallowance charge	124
Disallowance charge, after tax	$ 88