Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 90	$ 283
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	90	283
Total derivatives, not subject to a master netting or similar arrangement	0	1
Gross Amounts of Recognized Liabilities, Total	90	284
Derivative Liabilities	90	284
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	34	99
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	46
Net Amounts	56	138
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	16	61
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	16	61
Total derivatives, not subject to a master netting or similar arrangement	7	5
Gross Amounts of Recognized Liabilities, Total	23	66
Derivative Liabilities	23	66
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5	4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	11	57
Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	1	8
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1	8
Derivative Liabilities	1	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	0	6
Commodity | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	12	76
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	12	76
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	5	9
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	6
Net Amounts	7	61
Commodity | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	2	4
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	2	4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	2	4
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	0	0
Commodity | Over-the-counter | Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	0	6
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	0	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	0	6
Commodity | Exchange
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	19	120
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	19	120
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	19	80
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	40
Net Amounts	0	0
Interest rate | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	58	85
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
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
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	49	77
Interest rate | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	14	57
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	14	57
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	3	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	11	57
Foreign currency | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	1	2
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	0	0
Foreign currency | Over-the-counter | Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	1	2
Gross Amounts Offset in the Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	1	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0	0
Net Amounts	$ 0	$ 0