Investments (Narrative) (Detail) - USD ($) $ in Millions		1 Months Ended	3 Months Ended			6 Months Ended
		Aug. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Contributions to equity method affiliates						$ 134	$ 252
Investment in equity method affiliates				$ 1,710		1,710		$ 1,544	[1]
Other receivables	[2]			133		133		126	[1]
Liabilities, other deferred credits and other liabilities				17,006		17,006		16,631	[1]
Dominion Energy Gas Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Other receivables	[3]			22		22		15	[4]
Liabilities, other deferred credits and other liabilities				2,931		2,931		2,866	[4]
Equity in earnings on investments				5	$ 4	14	11
Dominion Energy Gas Holdings, LLC | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Investment in equity method affiliates				95		95		95
Equity method investment, balance carrying value				8		8		8
Equity in earnings on investments						14	11
Distributions received from investment						14	11
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Contributions to equity method affiliates				81	85	159	202
Atlantic Coast Pipeline | DETI
Schedule of Equity Method Investments [Line Items]
Revenue				60	$ 30	106	$ 61
Other receivables				19		19		12
Atlantic Coast Pipeline | Current Liabilities
Schedule of Equity Method Investments [Line Items]
Investment in equity method affiliates				33		33
NedPower Mount Storm LLC
Schedule of Equity Method Investments [Line Items]
Liabilities, other deferred credits and other liabilities				1		1		17
Catalyst Old River Hydroelectic Limited Partnership
Schedule of Equity Method Investments [Line Items]
Equity method investment, balance carrying value				0		0
Catalyst Old River Hydroelectic Limited Partnership | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment			$ 90
Gain on sale of equity method investments, net of tax			$ 65
Catalyst Old River Hydroelectic Limited Partnership | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage of limited partner interests		25.00%
Limited partnership interest sale transaction, expected proceeds		$ 90
Trading Securities
Schedule of Equity Method Investments [Line Items]
Rabbi trust securities				$ 114		$ 114		$ 112

[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 10 for amounts attributable to related parties.

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

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