Investments (Narrative) (Detail)		1 Months Ended					3 Months Ended		12 Months Ended
		Sep. 30, 2018 USD ($)	Dec. 31, 2016 USD ($)	Oct. 31, 2016 USD ($)	May 31, 2016 USD ($)	Sep. 30, 2014 Member mi	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Equity in earnings on investments										$ 197,000,000	$ 14,000,000	$ 111,000,000
Distributions received from investment										209,000,000	419,000,000	104,000,000
Carrying amount of investment that exceeded share of underlying equity							$ 161,000,000	$ 249,000,000		161,000,000	249,000,000
Equity method investment goodwill							176,000,000	73,000,000		176,000,000	73,000,000
Equity in earnings on investments										197,000,000	(18,000,000)	111,000,000
Additional membership percentage interest purchased				3.00%
Payment for purchase of equity interest				$ 14,000,000
Other receivables	[1]						331,000,000	126,000,000		331,000,000	126,000,000
Contributions to equity method affiliates										428,000,000	370,000,000	198,000,000
Impairment charge										403,000,000	15,000,000	4,000,000
Liabilities, other deferred credits and other liabilities							17,075,000,000	16,631,000,000		17,075,000,000	16,631,000,000
Finite Lived Equity Method Investment Basis Difference [Member]
Schedule of Equity Method Investments [Line Items]
Carrying amount of investment that exceeded share of underlying equity							146,000,000	15,000,000		146,000,000	15,000,000
Dominion Energy Gas Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Equity in earnings on investments										24,000,000	21,000,000	21,000,000
Other receivables	[2]						17,000,000	15,000,000		17,000,000	15,000,000
Impairment charge							219,000,000			346,000,000	16,000,000
Liabilities, other deferred credits and other liabilities							2,944,000,000	2,866,000,000		2,944,000,000	2,866,000,000
Dominion Energy Gas Holdings, LLC | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Distributions received from investment										28,000,000	24,000,000	22,000,000
Carrying amount of investment that exceeded share of underlying equity							8,000,000	8,000,000		8,000,000	8,000,000
Equity in earnings on investments										24,000,000	21,000,000	21,000,000
Trading Securities
Schedule of Equity Method Investments [Line Items]
Rabbi trust securities							111,000,000	112,000,000		111,000,000	112,000,000
Other Income [Member] | Dominion Energy Gas Holdings, LLC | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Percentage of non-controlling partnership interest sold					0.65%
Sales price of non-controlling partnership interest					$ 7,000,000
Amount of gain from sale					5,000,000
Amount of after tax gain from sale					$ 3,000,000
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Distributions received from investment										36,000,000	270,000,000
Contributions to equity method affiliates										414,000,000	310,000,000	184,000,000
Atlantic Coast Pipeline | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Project cost estimates increase									$ 250,000,000
Atlantic Coast Pipeline | DETI
Schedule of Equity Method Investments [Line Items]
Revenue										203,000,000	129,000,000	$ 95,000,000
Other receivables							13,000,000	12,000,000		$ 13,000,000	12,000,000
Atlantic Coast Pipeline | Minimum | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Project cost estimates									7,250,000,000
Atlantic Coast Pipeline | Maximum | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Project cost estimates									$ 7,750,000,000
Atlantic Coast Pipeline | Previous Minimum
Schedule of Equity Method Investments [Line Items]
Project cost estimates							6,000,000,000
Atlantic Coast Pipeline | Current Minimum
Schedule of Equity Method Investments [Line Items]
Project cost estimates							7,000,000,000
Atlantic Coast Pipeline | Previous Maximum
Schedule of Equity Method Investments [Line Items]
Project cost estimates							6,500,000,000
Atlantic Coast Pipeline | Current Maximum
Schedule of Equity Method Investments [Line Items]
Project cost estimates							$ 7,500,000,000
Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline | Distribution
Schedule of Equity Method Investments [Line Items]
Ownership interest (percentage)							48.00%			48.00%
Length of natural gas pipeline (in miles) | mi						600
Number of members | Member						3
Duration of contract						20 years
Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline | Distribution | Duke Energy
Schedule of Equity Method Investments [Line Items]
Ownership interest (percentage)							47.00%			47.00%
Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline | Distribution | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest (percentage)							5.00%			5.00%
Blue Racer
Schedule of Equity Method Investments [Line Items]
Amount of gain from sale							$ 546,000,000
Amount of after tax gain from sale							$ 390,000,000
Ownership interest percentage of limited partner interests							50.00%
Up-front cash consideration							$ 1,050,000,000
Additional deferred consideration, subject to increase for interest cost effective payable upon purchaser's availability of cash							150,000,000
Blue Racer | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Aggregate amount of contingent consideration, maximum													$ 300,000,000
Blue Racer | Oil and Gas Properties
Schedule of Equity Method Investments [Line Items]
Amount paid to repurchase portion of Western System from Blue Racer			$ 10,000,000
NedPower Mount Storm LLC
Schedule of Equity Method Investments [Line Items]
Liabilities, other deferred credits and other liabilities							1,000,000	17,000,000		$ 1,000,000	$ 17,000,000
NedPower Mount Storm LLC | Property, Plant and Equipment [Member]
Schedule of Equity Method Investments [Line Items]
Impairment charge								126,000,000
Impairment charge, after tax								$ 76,000,000
Fowler I Holdings LLC
Schedule of Equity Method Investments [Line Items]
Impairment charge							32,000,000
Impairment charge, after tax							20,000,000
Fair value of investment							$ 81,000,000			$ 81,000,000
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]
Amount of gain from sale		87,000,000
Amount of after tax gain from sale		$ 63,000,000

[1] See Note 9 for amounts attributable to related parties.

[2] See Note 24 for amounts attributable to related parties.