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				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	$ (36)		$ 16		$ 68		$ 131
Amount of Gain (Loss) Reclassified From AOCI to Income		(40)		25		(95)		91
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	48		(26)		141		(60)
Virginia Electric and Power Company
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[3]	4		(3)		13		(8)
Amount of Gain (Loss) Reclassified From AOCI to Income								(1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[4]	48		(26)		141		(60)
Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[5]	4		2		(6)		5
Amount of Gain (Loss) Reclassified From AOCI to Income		(7)		7		(22)		8
Electric fuel and other energy-related purchases
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income				(1)		8		1
Commodity contracts
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	(58)		8		(1)		139
Amount of Gain (Loss) Reclassified From AOCI to Income		(26)		31		(49)		115
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]	(5)		(10)		(11)		(5)
Amount of Gain (Loss) Reclassified From AOCI to Income		(3)		(2)		(8)		(4)
Commodity contracts | Operating Revenue
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(26)		32		(55)		114
Commodity contracts | Operating Revenue | Dominion Energy Gas Holdings, LLC
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(3)		(2)		(8)		(4)
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]	23	[6]	(4)		70	[6]	(18)
Amount of Gain (Loss) Reclassified From AOCI to Income		(12)	[6]	(16)		(36)	[6]	(39)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	48	[6]	(26)		141	[6]	(60)
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]	4	[7]	(3)	[7]	13		(8)
Amount of Gain (Loss) Reclassified From AOCI to Income								(1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[4]	48	[7]	(26)	[7]	141		(60)
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]	10	[8]			6
Amount of Gain (Loss) Reclassified From AOCI to Income		(2)	[8]	(1)	[8]	(4)		(3)
Foreign currency
Derivative Instruments Gain Loss [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	(1)	[9]	12		(1)	[9]	10
Amount of Gain (Loss) Reclassified From AOCI to Income		(2)	[9]	10		(10)	[9]	15
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]	(1)	[10]	12	[10]	(1)		10
Amount of Gain (Loss) Reclassified From AOCI to Income		$ (2)	[10]	$ 10	[10]	$ (10)		$ 15

[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.