Regulatory Assets and Liabilities (Schedule of Regulatory Assets) (Detail) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory assets-current	[1]	$ 616	$ 294	[2]
Regulatory assets-noncurrent		2,395	2,480	[2]
Total regulatory assets		3,011	2,774
Deferred cost of fuel used in electric generation
Regulatory Assets [Line Items]
Regulatory assets-current	[3]	344	23
Deferred rate adjustment clause costs
Regulatory Assets [Line Items]
Regulatory assets-current	[4]	89	70
Regulatory assets-noncurrent	[4]	372	401
Deferred nuclear refueling outage costs
Regulatory Assets [Line Items]
Regulatory assets-current	[5]	$ 76	54
Deferred nuclear refueling outage costs | Maximum
Regulatory Assets [Line Items]
Amortization period for deferred costs		18 months
Unrecovered gas costs
Regulatory Assets [Line Items]
Regulatory assets-current	[6]	$ 3	38
Other
Regulatory Assets [Line Items]
Regulatory assets-current		104	109
Regulatory assets-noncurrent		185	151
Unrecognized pension and other postretirement benefit costs
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[7]	1,296	1,336
PJM transmission rates
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[8]	237	222
Derivatives
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[9]	131	223
Utility reform legislation
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[10]	174	147
Virginia Electric and Power Company
Regulatory Assets [Line Items]
Regulatory assets-current	[1]	552	205	[11]
Regulatory assets-noncurrent		729	810	[11]
Total regulatory assets		1,281	1,015
Virginia Electric and Power Company | Deferred cost of fuel used in electric generation
Regulatory Assets [Line Items]
Regulatory assets-current	[3]	344	23
Virginia Electric and Power Company | Deferred rate adjustment clause costs
Regulatory Assets [Line Items]
Regulatory assets-current	[4]	56	56
Regulatory assets-noncurrent	[4]	296	312
Virginia Electric and Power Company | Deferred nuclear refueling outage costs
Regulatory Assets [Line Items]
Regulatory assets-current	[5]	76	54
Virginia Electric and Power Company | Other
Regulatory Assets [Line Items]
Regulatory assets-current		76	72
Regulatory assets-noncurrent		98	86
Virginia Electric and Power Company | PJM transmission rates
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[8]	237	222
Virginia Electric and Power Company | Derivatives
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[9]	98	190
Dominion Energy Gas Holdings, LLC
Regulatory Assets [Line Items]
Regulatory assets-current	[1]	35	26
Regulatory assets-noncurrent	[12]	526	511
Total regulatory assets		561	537
Dominion Energy Gas Holdings, LLC | Deferred rate adjustment clause costs
Regulatory Assets [Line Items]
Regulatory assets-current	[4]	33	14
Regulatory assets-noncurrent	[4]	76	89
Dominion Energy Gas Holdings, LLC | Unrecovered gas costs
Regulatory Assets [Line Items]
Regulatory assets-current	[6]	0	8
Dominion Energy Gas Holdings, LLC | Other
Regulatory Assets [Line Items]
Regulatory assets-current		2	4
Regulatory assets-noncurrent		25	17
Dominion Energy Gas Holdings, LLC | Unrecognized pension and other postretirement benefit costs
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[7]	251	258
Dominion Energy Gas Holdings, LLC | Utility reform legislation
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[10]	$ 174	$ 147

[1] Current regulatory assets are presented in other current assets in Dominion Energy Gas’ 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] Reflects deferred fuel expenses for the Virginia and North Carolina jurisdictions of Dominion Energy and Virginia Power’s generation operations.

[4] Primarily reflects deferrals under the electric transmission FERC formula rate and the deferral of costs associated with certain current and prospective rider projects net of income taxes refundable from the 2017 Tax Reform Act for Virginia Power and deferrals of costs associated with certain current and prospective rider projects for Dominion Energy Gas. See Note 13 for more information.

[5] Legislation enacted in Virginia in April 2014 requires Virginia Power to defer operation and maintenance costs incurred in connection with the refueling of any nuclear-powered generating plant. These deferred costs will be amortized over the refueling cycle, not to exceed 18 months.

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

[7] Represents unrecognized pension and other postretirement employee benefit costs expected to be recovered or refunded through future rates generally over the expected remaining service period of plan participants by certain of Dominion Energy's and Dominion Energy Gas' rate-regulated subsidiaries.

[8] Reflects amounts related to the PJM transmission cost allocation matter. See Note 13 for more information.

[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] Ohio legislation under House Bill 95, which became effective in September 2011. This law updates natural gas legislation by enabling gas companies to include more up-to-date cost levels when filing rate cases. It also allows gas companies to seek approval of capital expenditure plans under which gas companies can recognize carrying costs on associated capital investments placed in service and can defer the carrying costs plus depreciation and property tax expenses for recovery from ratepayers in the future.

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

[12] Noncurrent regulatory assets are presented in other deferred charges and other assets in Dominion Energy Gas’ Consolidated Balance Sheets.