Derivatives and Hedge Accounting Activities (Gains and Losses on Derivatives in Cash Flow Hedging Relationships) (Detail) - Cash Flow Hedges - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	$ (44)		$ 45		$ 104		$ 115
Amount of Gain (Loss) Reclassified From AOCI to Income		(44)		29		(55)		66
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	25		(42)		93		(34)
Virginia Electric and Power Company
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[3]	2		(5)		9		(5)
Amount of Gain (Loss) Reclassified From AOCI to Income				(1)				(1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[4]	25		(42)		93		(34)
Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[5]	(27)		18		(10)		3
Amount of Gain (Loss) Reclassified From AOCI to Income		(19)		19		(15)		1
Electric fuel and other energy-related purchases
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income				2		7		2
Commodity contracts
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	(39)		44		58		131
Amount of Gain (Loss) Reclassified From AOCI to Income		(16)		21		(23)		83
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	0				0
Commodity contracts | Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[5]	(10)		2		(6)		4
Amount of Gain (Loss) Reclassified From AOCI to Income		(2)		1		(5)		(3)
Commodity contracts | Operating Revenue
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(16)		19		(28)		81
Commodity contracts | Operating Revenue | Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(2)		1		(5)		(3)
Commodity contracts | Purchased Gas
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income						(2)
Interest rate
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	9	[6]	(15)		47	[6]	(14)
Amount of Gain (Loss) Reclassified From AOCI to Income		(12)	[6]	(11)		(24)	[6]	(23)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	25	[6]	(42)		93	[6]	(34)
Interest rate | Virginia Electric and Power Company
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[3]	2	[7]	(5)	[7]	9		(5)
Amount of Gain (Loss) Reclassified From AOCI to Income				(1)	[7]			(1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[4]	25	[7]	(42)	[7]	93		(34)
Interest rate | Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[5]	(3)	[8]			(3)
Amount of Gain (Loss) Reclassified From AOCI to Income		(1)	[8]	(1)	[8]	(2)		(2)
Foreign currency
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	(14)	[9]	16		(1)	[9]	(2)
Amount of Gain (Loss) Reclassified From AOCI to Income		(16)	[9]	19		(8)	[9]	6
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2],[9]	0				0
Foreign currency | Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[5]	(14)	[10]	16	[10]	(1)		(1)
Amount of Gain (Loss) Reclassified From AOCI to Income		$ (16)	[10]	$ 19	[10]	$ (8)		$ 6

[1] Amounts deferred into AOCI have no associated effect in Dominion Energy’s Consolidated Statements of Income.

[2] Represents net derivative activity deferred into and amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/liabilities have no associated effect in Dominion Energy’s Consolidated Statements of Income.

[3] Amounts deferred into AOCI have no associated effect in Virginia Power’s Consolidated Statements of Income.

[4] Represents net derivative activity deferred into and amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/liabilities have no associated effect in Virginia Power’s Consolidated Statements of Income.

[5] Amounts deferred into AOCI have no associated effect in Dominion Energy Gas’ Consolidated Statements of Income.

[6] Amounts recorded in Dominion Energy’s Consolidated Statements of Income are classified in interest and related charges.

[7] Amounts recorded in Virginia Power’s Consolidated Statements of Income are classified in interest and related charges.

[8] Amounts recorded in Dominion Energy Gas’ Consolidated Statements of Income are classified in interest and related charges

[9] Amounts recorded in Dominion Energy’s Consolidated Statements of Income are classified in other income.

[10] Amounts recorded in Dominion Energy Gas’ Consolidated Statements of Income are classified in other income.