Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 118	$ 283
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	118	283
Total derivatives, not subject to a master netting or similar arrangement		1
Gross Amounts of Recognized Liabilities, Total	118	284
Derivative Liabilities	118	284
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	42	99
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	11	46
Net Amounts	65	138
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	9	61
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	9	61
Total derivatives, not subject to a master netting or similar arrangement	5	5
Gross Amounts of Recognized Liabilities, Total	14	66
Derivative Liabilities	14	66
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	6	4
Net Amounts	3	57
Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	16	8
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	16	8
Derivative Liabilities	16	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	6	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	10	6
Commodity contracts \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	23	76
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	23	76
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	7	9
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		6
Net Amounts	16	61
Commodity contracts \| Exchange
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	32	120
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	32	120
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	21	80
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	11	40
Commodity contracts \| Virginia Electric and Power Company \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	3	4
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	3	4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	3	4
Commodity contracts \| Dominion Energy Gas Holdings, LLC \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	7	6
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	7	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	7	6
Interest rate \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	58	85
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	58	85
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	9	8
Net Amounts	49	77
Interest rate \| Virginia Electric and Power Company \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	6	57
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	6	57
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	3
Net Amounts	3	57
Interest rate \| Dominion Energy Gas Holdings, LLC \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	4	0
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	4	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	3	0
Foreign currency \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	5	2
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	5	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5	2
Foreign currency \| Dominion Energy Gas Holdings, LLC \| Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	5	2
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	5	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5	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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