Accumulated Other Comprehensive Income (Schedule of Reclassifications out of AOCI by Component Net of Tax) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue	[1]	$ (3,088)	$ (2,813)	$ (6,554)	$ (6,197)
Interest and related charges		361	308	675	600
Other income		(185)	(108)	(285)	(270)
Income from operations including noncontrolling interests before income tax expense		(566)	(553)	(1,227)	(1,502)
Income tax expense		88	136	223	411
Purchased gas		64	112	404	417
Income tax expense		(11)	11	(14)	25
Income from continuing operations net of tax	[2]	33	(18)	41	(41)
Income tax expense		(1)	2	(1)	18
Income from continuing operations net of tax	[3]		(4)	1	(32)
Virginia Electric and Power Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue	[4]	(1,829)	(1,747)	(3,577)	(3,578)
Interest and related charges	[4]	126	125	258	245
Other income		(21)	(13)	(24)	(44)
Income from operations including noncontrolling interests before income tax expense		(428)	(501)	(663)	(1,065)
Income tax expense		89	183	140	391
Income from continuing operations net of tax	[5]		1		1
Dominion Energy Gas Holdings, LLC
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Operating revenue	[6]	(459)	(422)	(985)	(912)
Interest and related charges	[6]	26	24	51	47
Other income		(32)	(27)	(65)	(52)
Income from operations including noncontrolling interests before income tax expense		(18)	(122)	(236)	(287)
Income tax expense		3	45	55	102
Purchased gas	[6]		38	29	81
Income tax expense		(5)	7	(4)
Income from continuing operations net of tax	[7]	14	(12)	11	(1)
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		623	498	1,367	1,073
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]	508	409	1,099	865
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		44	(29)	55	(66)
Income tax expense		(11)	11	(14)	25
Income from continuing operations including noncontrolling interests		33	(18)	41	(41)
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		1
Income from continuing operations net of tax			1		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		19	(19)	15	(1)
Income tax expense		(5)	7	(4)
Income from continuing operations including noncontrolling interests		14	(12)	11	(1)
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		16	(19)	28	(81)
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		2	(1)	5	3
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			(2)	(7)	(2)
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	11	24	23
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		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		1	1	2	2
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		16	(19)	8	(6)
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		16	(19)	8	(6)
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		1	(11)	2	(64)
Impairment			5		14
Income from operations including noncontrolling interests before income tax expense		1	(6)	2	(50)
Income tax expense		(1)	2	(1)	18
Income from continuing operations including noncontrolling interests			(4)	1	(32)
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			(1)		(7)
Impairment					1
Income from operations before income tax expense			(1)		(6)
Income tax expense					2
Income from continuing operations net of tax			(1)		(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)	(11)	(9)
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		24	21	50	42
Unrecognized pension and other postretirement benefit costs, income tax expense		(7)	(10)	(8)	(18)
Unrecognized pension and other postretirement benefit costs, net of tax		17	11	42	24
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		1	2	3	3
Unrecognized pension and other postretirement benefit costs, income tax expense				(1)	(1)
Unrecognized pension and other postretirement benefit costs, net of tax		1	2	2	2
Amortization of actuarial losses | Amounts Reclassified From AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income		29	26	61	51
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		$ 1	$ 2	$ 3	$ 3

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

[2] Net of $(11) million and $11 million tax for the three months ended June 30, 2018 and 2017, respectively, and net of $(14) million and $25 million tax for the six months ended June 30, 2018 and 2017, respectively.

[3] Net of $(1) million and $2 million tax for the three months ended June 30, 2018 and 2017, respectively, and net of $(1) million and $18 million tax for the six months ended June 30, 2018 and 2017, respectively.

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

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

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

[7] Net of $(5) million and $7 million tax for the three months ended June 30, 2018 and 2017, respectively, and net of $(4) million and $— million tax for the six months ended June 30, 2018 and 2017, respectively.