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
		Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	$ 148	$ 70
Amount of Gain (Loss) Reclassified From AOCI to Income		(11)	37
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	68	8
Virginia Electric and Power Company
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[3]	7
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[4]	68	8
Dominion Energy Gas Holdings, LLC
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[5]	17	(16)
Amount of Gain (Loss) Reclassified From AOCI to Income		4	(18)
Electric Fuel and Other Energy-Related Purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		7	(1)
Commodity
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1]	97	87
Amount of Gain (Loss) Reclassified From AOCI to Income		(7)	62
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2]	0	0
Commodity | 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
Amount of Gain (Loss) Reclassified From AOCI to Income		(3)	(3)
Commodity | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(12)	62
Commodity | Operating Revenue | Dominion Energy Gas Holdings, LLC
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(3)	(3)
Commodity | Purchased Gas
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified From AOCI to Income		(2)	1
Interest rate
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1],[6]	38	1
Amount of Gain (Loss) Reclassified From AOCI to Income	[6]	(12)	(11)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[2],[6]	68	8
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],[7]	7
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[4],[7]	68	8
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],[8]	0
Amount of Gain (Loss) Reclassified From AOCI to Income	[8]	(1)	(1)
Foreign currency
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	[1],[9]	13	(18)
Amount of Gain (Loss) Reclassified From AOCI to Income	[9]	8	(14)
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],[10]	13	(18)
Amount of Gain (Loss) Reclassified From AOCI to Income	[10]	$ 8	$ (14)

[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.