Regulatory Assets and Liabilities (Schedule of Regulatory Liabilities) (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[1]	$ 335	$ 193
Regulatory liabilities-noncurrent		7,146	6,916	[2]
Total regulatory liabilities		7,481	7,109
Provision for future cost of removal and AROs
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[3]	101	101
Regulatory liabilities-noncurrent	[3]	1,414	1,384
Reserve for rate credits to customers
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[4]	61
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities-current		93	92
Regulatory liabilities-noncurrent		403	353
Nuclear decommissioning trust
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[5]	1,241	1,121
Income taxes refundable through future rates
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[6]	4,088	4,058
Cost-of-service impact of 2017 Tax Reform Act
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[7]	80
Virginia Electric and Power Company
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[1]	250	127
Regulatory liabilities-noncurrent		4,890	4,760	[8]
Total regulatory liabilities		5,140	4,887
Virginia Electric and Power Company | Reserve for rate credits to customers
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[4]	61
Virginia Electric and Power Company | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities-current		42	47
Regulatory liabilities-noncurrent		112	74
Virginia Electric and Power Company | Nuclear decommissioning trust
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[5]	1,241	1,121
Virginia Electric and Power Company | Income taxes refundable through future rates
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[6]	2,561	2,581
Virginia Electric and Power Company | Cost-of-service impact of 2017 Tax Reform Act
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[7]	67
Virginia Electric and Power Company | Provision for future cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[3]	80	80
Regulatory liabilities-noncurrent	[3]	938	915
Virginia Electric and Power Company | Derivatives
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[9]	38	69
Dominion Energy Gas Holdings, LLC
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[1]	32	38
Regulatory liabilities-noncurrent		1,309	1,227	[10]
Total regulatory liabilities		1,341	1,265
Dominion Energy Gas Holdings, LLC | Provision for future cost of removal and AROs
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[3]	13	13
Regulatory liabilities-noncurrent	[3]	164	160
Dominion Energy Gas Holdings, LLC | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities-current		9	5
Regulatory liabilities-noncurrent		92	69
Dominion Energy Gas Holdings, LLC | Income taxes refundable through future rates
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[6]	1,038	998
Dominion Energy Gas Holdings, LLC | Cost-of-service impact of 2017 Tax Reform Act
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[7]	15
Dominion Energy Gas Holdings, LLC | PIPP
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[11]	4	$ 20
Dominion Energy Gas Holdings, LLC | Overrecovered gas costs
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[12]	$ 6

[1] Current regulatory liabilities are presented in other current liabilities in the Companies’ Consolidated Balance Sheets.

[2] Dominion Energy’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

[3] Rates charged to customers by the Companies’ regulated businesses include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement.

[4] Charge associated with Virginia legislation enacted in March 2018 that requires one-time rate credits of certain amounts to utility customers. See Note 13 for more information.

[5] Primarily reflects a regulatory liability representing amounts collected from Virginia jurisdictional customers and placed in external trusts (including income, losses and changes in fair value thereon) for the future decommissioning of Virginia Power’s utility nuclear generation stations, in excess of the related AROs.

[6] Amounts recorded to pass the effect of reduced income taxes from the 2017 Tax Reform Act to customers in future periods, which will reverse at the weighted average tax rate that was used to build the reserves over the remaining book life of the property, net of amounts to be recovered through future rates to pay income taxes that become payable when rate revenue is provided to recover AFUDC-equity.

[7] Balance refundable to customers related to the decrease in revenue requirements for recovery of income taxes at the Companies’ regulated electric generation and electric and natural gas distribution operations. See Note 13 for more information.

[8] Virginia Power’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

[9] For jurisdictions subject to cost-based rate regulation, changes in the fair value of derivative instruments result in the recognition of regulatory assets or regulatory liabilities as they are expected to be recovered from or refunded to customers.

[10] Dominion Energy Gas’ Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

[11] Under PIPP, eligible customers can make reduced payments based on their ability to pay. The difference between the customer’s total bill and the PIPP plan amount is deferred and collected or returned annually under the PIPP rate adjustment clause according to East Ohio tariff provisions.

[12] Reflects unrecovered or overrecovered gas costs at regulated gas operations, which are recovered or refunded through filings with the applicable regulatory authority.