Accumulated Other Comprehensive Income (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue	[1]	$ (3,466)	$ (3,384)
Purchased gas		340	305
Electric fuel and other energy-related purchases		744	575
Interest and related charges		314	292
Other income		(100)	(162)
Income from operations including noncontrolling interests before income tax expense		(661)	(949)
Income tax expense		135	275
Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue	[2]	(1,748)	(1,831)
Electric fuel and other energy-related purchases	[2]	591	456
Interest and related charges	[2]	132	120
Other income		(3)	(31)
Income from operations including noncontrolling interests before income tax expense		(235)	(564)
Income tax expense		51	208
Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue	[3]	(526)	(490)
Purchased gas	[3]	29	43
Interest and related charges	[3]	25	23
Other income		(33)	(25)
Income from operations including noncontrolling interests before income tax expense		(218)	(165)
Income tax expense		52	57
Deferred (gains) and losses on derivatives-hedging activities: | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from operations including noncontrolling interests before income tax expense		11	(37)
Income tax expense		(3)	14
Income from continuing operations including noncontrolling interests		8	(23)
Deferred (gains) and losses on derivatives-hedging activities: | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from operations including noncontrolling interests before income tax expense		(4)	18
Income tax expense		1	(7)
Income from continuing operations including noncontrolling interests		(3)	11
Deferred (gains) and losses on derivatives-hedging activities: | Commodity contracts | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue		12	(62)
Purchased gas		2	(1)
Electric fuel and other energy-related purchases		(7)	1
Deferred (gains) and losses on derivatives-hedging activities: | Commodity contracts | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating revenue		3	3
Deferred (gains) and losses on derivatives-hedging activities: | Interest rate contracts | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and related charges		12	11
Deferred (gains) and losses on derivatives-hedging activities: | Interest rate contracts | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and related charges		1	1
Deferred (gains) and losses on derivatives-hedging activities: | Foreign currency | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		(8)	14
Deferred (gains) and losses on derivatives-hedging activities: | Foreign currency | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		(8)	14
Unrealized (gains) and losses on investment securities: | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized (gain) loss on sale of securities		1	(53)
Impairment			9
Income from operations including noncontrolling interests before income tax expense		1	(44)
Income tax expense			16
Income from continuing operations including noncontrolling interests		1	(28)
Unrealized (gains) and losses on investment securities: | Amounts Reclassified From AOCI | Virginia Electric and Power Company
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized (gain) loss on sale of securities			(6)
Impairment			1
Income from operations including noncontrolling interests before income tax expense			(5)
Income tax expense			2
Income from continuing operations including noncontrolling interests			(3)
Amortization of prior-service costs (credits) | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		(5)	(4)
Unrecognized pension and other postretirement benefit costs:
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		26	21
Unrecognized pension and other postretirement benefit costs, income tax expense		(1)	(8)
Unrecognized pension and other postretirement benefit costs, net of tax		25	13
Unrecognized pension and other postretirement benefit costs: | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		2	1
Unrecognized pension and other postretirement benefit costs, income tax expense		(1)	(1)
Unrecognized pension and other postretirement benefit costs, net of tax		1
Amortization of actuarial losses | Amounts Reclassified From AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		31	25
Amortization of actuarial losses | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income		$ 2	$ 1

[1] See Note 10 for amounts attributable to related parties.

[2] See Note 18 for amounts attributable to affiliates.

[3] See Note 18 for amounts attributable to related parties.