Income Taxes (Narrative) (Detail) - USD ($) $ in Millions		1 Months Ended	10 Months Ended	12 Months Ended
		Jun. 30, 2017	Oct. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Federal statutory income tax rate				21.00%	21.00%	35.00%
State deferred income tax expense				$ (93.0)	$ (1.0)	$ 132.0
Current federal income taxes				135.0	63.0	(27.0)
Taxes charged to common shareholders' equity				215.0
Deferred income tax expense	[1]				46.0	(851.0)
Increase (Decrease) to deferred income tax expense					23.0
Increase (Decrease) in regulatory liabilities					35.0	4,200.0
Decrease in unrecognized tax benefits due to settlement				7.0	6.0	23.0
Unrecognized tax benefits that would impact effective tax rate				141.0	37.0	31.0
Decrease in accumulated deferred income tax liability						3,100.0
Increase (decrease) in deferred tax asset						1,100.0
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits				3.0	5.0	(9.0)
Operating Loss Carryforwards				4,435.0
Income tax expense (benefit)				351.0	580.0	(30.0)
Deferred tax liabilities noncurrent				6,277.0	5,116.0
Regulatory liability noncurrent				11,001.0	6,840.0
Dominion Cove Point L N G L P [Member]
Income Taxes [Line Items]
Current federal income taxes				362.0
Benefit for deferred income taxes				147.0
Federal tax credits				$ 208.0
Ownership interest percentage of limited partner interests				25.00%
SCANA
Income Taxes [Line Items]
Deferred income tax expense				$ 194.0
Noncurrent Liabilities [Member]
Income Taxes [Line Items]
Increase (Decrease) in regulatory liabilities					$ 23.0
Discontinued Operations [Member]
Income Taxes [Line Items]
Income tax expense (benefit)			$ 33.0			5.0
Deferred tax liabilities noncurrent						$ 0.4
Carryback claim for specified liability losses involving prior tax years
Income Taxes [Line Items]
Current federal income taxes				47.0
Maximum
Income Taxes [Line Items]
State deferred income tax expense				1.0
Decrease in Unrecognized tax benefits due to settlement negotiations and expiration of statutes of limitations				86.0
Amount that earnings could potentially increase if changes were to occur				23.0
Federal
Income Taxes [Line Items]
Operating Loss Carryforwards				$ 1,361.0
Virginia Electric and Power Company
Income Taxes [Line Items]
Federal statutory income tax rate				21.00%	21.00%	35.00%
State deferred income tax expense				$ 22.0	$ 55.0	$ 59.0
Current federal income taxes				344.0	76.0	505.0
Deferred income tax expense	[1]			0.0	21.0	(93.0)
Increase (Decrease) to deferred income tax expense					23.0
Increase (Decrease) in regulatory liabilities					31.0	2,600.0
Decrease in unrecognized tax benefits due to settlement		$ 8.0		2.0	1.0	8.0
Unrecognized tax benefits that would impact effective tax rate		2.0		1.0	2.0	3.0
Interest income		$ 11.0
Decrease in accumulated deferred income tax liability						1,900.0
Increase (decrease) in deferred tax asset						700.0
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits				(2.0)		(6.0)
Income tax expense (benefit)				264.0	300.0	$ 774.0
Deferred tax liabilities noncurrent				2,962.0	3,017.0
Regulatory liability noncurrent				$ 5,074.0	$ 4,647.0
Dominion Energy Gas Holdings, LLC
Income Taxes [Line Items]
Federal statutory income tax rate				21.00%	21.00%	35.00%
State deferred income tax expense				$ (10.0)	$ (17.0)	$ 5.0
Current federal income taxes				147.0	(196.0)	88.0
Deferred income tax expense	[1]				(6.0)	(246.0)
Increase (Decrease) to deferred income tax expense					(5.0)
Increase (Decrease) in regulatory liabilities					(8.0)	1,100.0
Decrease in unrecognized tax benefits due to settlement				0.0	0.0	7.0
Decrease in accumulated deferred income tax liability						800.0
Increase (decrease) in deferred tax asset						300.0
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits					(1.0)	(5.0)
Operating Loss Carryforwards				1.0
Income tax expense (benefit)				101.0	124.0	(65.0)
Deferred tax liabilities noncurrent				1,288.0	1,330.0
Regulatory liability noncurrent				800.0	765.0
Dominion Energy Gas Holdings, LLC | Discontinued Operations [Member]
Income Taxes [Line Items]
Increase (Decrease) to deferred income tax expense					8.0
Increase (Decrease) in regulatory liabilities					10.0
Income tax expense (benefit)					91.0
Deferred tax liabilities noncurrent						0.1
Regulatory liability noncurrent						0.5
Dominion Energy Gas Holdings, LLC | Maximum
Income Taxes [Line Items]
Unrecognized tax benefits that would impact effective tax rate				2.0	2.0	$ 2.0
Decrease in Unrecognized tax benefits due to settlement negotiations and expiration of statutes of limitations				1.0
Amount that earnings could potentially increase if changes were to occur				1.0
Dominion Energy Gas Holdings, LLC | Maximum | Discontinued Operations [Member]
Income Taxes [Line Items]
Income tax expense (benefit)					$ 1.0
Dominion Energy Gas Holdings, LLC | Federal
Income Taxes [Line Items]
Deferred income tax expense				$ 48.0

[1] The 2017 Tax Reform Act impact for Dominion Energy Gas includes an expense of $8 million for the year ended December 31, 2018 and a benefit of $93 million for the year ended December 31, 2017 arising from discontinued operations.