Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 145	$ 283
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	145	283
Total derivatives, not subject to a master netting or similar arrangement		1
Gross Amounts of Recognized Liabilities, Total	145	284
Derivative Liabilities	145	284
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	51	99
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	39	46
Net Amounts	55	138
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	5	61
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	5	61
Total derivatives, not subject to a master netting or similar arrangement	3	5
Gross Amounts of Recognized Liabilities, Total	8	66
Derivative Liabilities	8	66
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5	4
Net Amounts		57
Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	13	8
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	13	8
Derivative Liabilities	13	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	4	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	9	6
Commodity contracts \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	32	76
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	32	76
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	10	9
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		6
Net Amounts	22	61
Commodity contracts \| Exchange
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	68	120
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	68	120
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	29	80
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	39	40
Commodity contracts \| Virginia Electric and Power Company \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	5	4
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	5	4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5	4
Commodity contracts \| Dominion Energy Gas Holdings, LLC \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	9	6
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	9	6
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	0	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	9	6
Interest rate \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	42	85
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	42	85
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	9	8
Net Amounts	33	77
Interest rate \| Virginia Electric and Power Company \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities		57
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet		57
Net Amounts		57
Interest rate \| Dominion Energy Gas Holdings, LLC \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	1	0
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	0	0
Foreign currency \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	3	2
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	3	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	3	2
Foreign currency \| Dominion Energy Gas Holdings, LLC \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	3	2
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	3	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	3	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	$ 0	$ 0

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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