Investments (Narrative) (Detail) - USD ($)			1 Months Ended		3 Months Ended			9 Months Ended
		Mar. 31, 2019	Oct. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Contributions to equity method affiliates								$ 282,000,000	$ 343,000,000
Investment in equity method affiliates				$ 1,858,000,000		$ 1,858,000,000		1,858,000,000		$ 1,544,000,000	[1]
Other receivables				132,000,000		132,000,000		132,000,000		126,000,000	[1]
Liabilities, other deferred credits and other liabilities				17,256,000,000		17,256,000,000		17,256,000,000		16,631,000,000	[1]
Dominion Energy Gas Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Other receivables	[2]			18,000,000		18,000,000		18,000,000		15,000,000	[3]
Liabilities, other deferred credits and other liabilities				3,007,000,000		3,007,000,000		3,007,000,000		2,866,000,000	[3]
Equity in earnings on investments						4,000,000	$ 4,000,000	18,000,000	15,000,000
Dominion Energy Gas Holdings, LLC | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Investment in equity method affiliates				93,000,000		93,000,000		93,000,000		95,000,000
Equity in earnings on investments								18,000,000	15,000,000
Distributions received from investment								20,000,000	17,000,000
Equity method investment, balance carrying value				8,000,000		8,000,000		$ 8,000,000		8,000,000
Blue Racer
Schedule of Equity Method Investments [Line Items]
Equity method investment contingent consideration, description								This will result in a gain when realizable. Also, the purchaser agreed to pay additional consideration contingent upon the achievement of certain financial performance milestones of Blue Racer from 2019 through 2021. Pursuant to the purchase agreement, the aggregate will not exceed $300 million,
Blue Racer | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Up-front cash consideration					$ 1,050,000,000
Gain on sale of equity method investment					380,000,000
Gain on sale of equity method investments, net of tax					$ 230,000,000
Additional deferred consideration, subject to increase for interest cost effective payable upon purchaser's availability of cash		$ 150,000,000
Aggregate amount of contingent consideration, maximum		$ 300,000,000
Blue Racer | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage of limited partner interests			50.00%
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Contributions to equity method affiliates						147,000,000	84,000,000	$ 306,000,000	286,000,000
Atlantic Coast Pipeline | DETI
Schedule of Equity Method Investments [Line Items]
Revenue						50,000,000	$ 32,000,000	156,000,000	$ 93,000,000
Other receivables				15,000,000		15,000,000		15,000,000		12,000,000
Atlantic Coast Pipeline | Current Liabilities
Schedule of Equity Method Investments [Line Items]
Investment in equity method affiliates				37,000,000		37,000,000		37,000,000
NedPower Mount Storm LLC
Schedule of Equity Method Investments [Line Items]
Liabilities, other deferred credits and other liabilities				$ 0		0		0		17,000,000
Catalyst Old River Hydroelectric Limited Partnership
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage of limited partner interests				25.00%
Limited partnership interest sale transaction, proceeds received				$ 91,000,000
Catalyst Old River Hydroelectric Limited Partnership | Other Income [Member]
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment				87,000,000
Gain on sale of equity method investments, net of tax				63,000,000
Trading Securities
Schedule of Equity Method Investments [Line Items]
Rabbi trust securities				$ 114,000,000		$ 114,000,000		$ 114,000,000		$ 112,000,000

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

[2] See Note 18 for amounts attributable to related parties.

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