Accumulated Other Comprehensive Income (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue	[1]	$ (3,451)	$ (3,179)	$ (10,005)	$ (9,376)
Interest and related charges		378	305	1,053	905
Other income		(373)	(121)	(658)	(391)
Income from operations including noncontrolling interests before income tax expense		(1,145)	(968)	(2,372)	(2,470)
Income tax expense		262	272	485	683
Income tax expense		(10)	10	(24)	35
Income from continuing operations net of tax	[2]	30	(15)	71	(56)
Income tax expense			2	(1)	20
Income from continuing operations net of tax	[3]	3	(4)	4	(36)
Virginia Electric and Power Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue	[4]	(2,232)	(2,154)	(5,809)	(5,732)
Interest and related charges	[4]	130	128	388	373
Other income		(25)	(13)	(49)	(57)
Income from operations including noncontrolling interests before income tax expense		(651)	(732)	(1,314)	(1,797)
Income tax expense		131	273	271	664
Income from continuing operations net of tax	[5]				1
Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue	[6]	(423)	(401)	(1,408)	(1,313)
Interest and related charges	[6]	28	25	79	72
Other income		(34)	(27)	(99)	(79)
Income from operations including noncontrolling interests before income tax expense		(192)	(191)	(428)	(478)
Income tax expense		56	74	111	176
Income tax expense		(2)	3	(6)	3
Income from continuing operations net of tax	[7]	5	(4)	16	(5)
Electric Fuel and Other Energy-Related Purchases
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Electric fuel and other energy-related purchases		761	638	2,128	1,711
Electric Fuel and Other Energy-Related Purchases | Virginia Electric and Power Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Electric fuel and other energy-related purchases	[4]	648	549	1,747	1,414
Deferred (gains) and losses on derivatives-hedging activities: | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income from operations including noncontrolling interests before income tax expense		40	(25)	95	(91)
Income tax expense		(10)	10	(24)	35
Income from continuing operations including noncontrolling interests		30	(15)	71	(56)
Deferred (gains) and losses on derivatives-hedging activities: | Amounts Reclassified From AOCI | Virginia Electric and Power Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income from operations before income tax expense					1
Income from continuing operations net of tax					1
Deferred (gains) and losses on derivatives-hedging activities: | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income from operations including noncontrolling interests before income tax expense		7	(7)	22	(8)
Income tax expense		(2)	3	(6)	3
Income from continuing operations including noncontrolling interests		5	(4)	16	(5)
Deferred (gains) and losses on derivatives-hedging activities: | Commodity contracts | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue		26	(32)	55	(114)
Purchased gas				2
Deferred (gains) and losses on derivatives-hedging activities: | Commodity contracts | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue		3	2	8	4
Deferred (gains) and losses on derivatives-hedging activities: | Commodity contracts | Amounts Reclassified From AOCI | Electric Fuel and Other Energy-Related Purchases
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Electric fuel and other energy-related purchases			1	(8)	(1)
Deferred (gains) and losses on derivatives-hedging activities: | Interest rate contracts | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest and related charges		12	16	36	39
Deferred (gains) and losses on derivatives-hedging activities: | Interest rate contracts | Amounts Reclassified From AOCI | Virginia Electric and Power Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest and related charges					1
Deferred (gains) and losses on derivatives-hedging activities: | Interest rate contracts | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest and related charges		2	1	4	3
Deferred (gains) and losses on derivatives-hedging activities: | Foreign currency | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income		2	(10)	10	(15)
Deferred (gains) and losses on derivatives-hedging activities: | Foreign currency | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income		2	(10)	10	(15)
Unrealized (gains) and losses on investment securities: | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Realized (gain) loss on sale of securities		3	(10)	5	(74)
Impairment			4		18
Income from operations including noncontrolling interests before income tax expense		3	(6)	5	(56)
Income tax expense			2	(1)	20
Income from continuing operations including noncontrolling interests		3	(4)	4	(36)
Unrealized (gains) and losses on investment securities: | Amounts Reclassified From AOCI | Virginia Electric and Power Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Realized (gain) loss on sale of securities					(8)
Impairment					2
Income from operations before income tax expense					(6)
Income tax expense					2
Income from continuing operations net of tax					(4)
Amortization of prior-service costs (credits) | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income		(5)	(5)	(16)	(16)
Unrecognized pension and other postretirement benefit costs:
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		25	21	75	63
Unrecognized pension and other postretirement benefit costs, income tax expense		(7)	(7)	(15)	(25)
Unrecognized pension and other postretirement benefit costs, net of tax		18	14	60	38
Unrecognized pension and other postretirement benefit costs: | Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Unrecognized pension and other postretirement benefit costs, before tax		2	2	5	5
Unrecognized pension and other postretirement benefit costs, income tax expense			(1)	(1)	(2)
Unrecognized pension and other postretirement benefit costs, net of tax		2	1	4	3
Amortization of actuarial losses | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income		30	26	91	79
Amortization of actuarial losses | Amounts Reclassified From AOCI | Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income		$ 2	$ 2	$ 5	$ 5

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

[2] Net of $(10) million and $10 million tax for the three months ended September 30, 2018 and 2017, respectively, and net of $(24) million and $35 million tax for the nine months ended September 30, 2018 and 2017, respectively.

[3] Net of $— million and $2 million tax for the three months ended September 30, 2018 and 2017, respectively, and net of $(1) million and $20 million tax for the nine months ended September 30, 2018 and 2017, respectively.

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

[5] Net of $— million tax for both the three and nine months ended September 30, 2018 and 2017.

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

[7] Net of $(2) million and $3 million tax for the three months ended September 30, 2018 and 2017, respectively, and net of $(6) million and $3 million tax for the nine months ended September 30, 2018 and 2017, respectively.