Income Taxes (Narrative) (Detail) - USD ($) $ in Millions		12 Months Ended
	Nov. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
State deferred income tax expense (benefit)		$ 72	$ (50)	$ 34
Deferred income tax expense		0	0	46
Current federal income taxes		(395)	(36)	376
Taxes charged to common shareholders' equity			215
Income tax expense	$ 336	$ 83	$ 209	$ 522
Federal statutory income tax rate		21.00%	21.00%	21.00%	35.00%
Deferred income tax expense		$ 439	$ 186	$ 146
Increase (Decrease) to deferred income tax expense			(5)	23
Increase (Decrease) in regulatory liabilities			(8)
Income tax benefit associated with remeasurement of state deferred taxes		(44)	(119)	(92)
Income tax expense attributable to noncontrolling interest		55
Unrecognized tax benefits that would impact effective tax rate		140	141	37
Maximum
Income Taxes [Line Items]
Decrease in Unrecognized tax benefits due to settlement negotiations and expiration of statutes of limitations		69
Amount that earnings could potentially increase if changes were to occur		7
Virginia Electric and Power Company
Income Taxes [Line Items]
State deferred income tax expense (benefit)		7	22	55
Deferred income tax expense		0	0	21
Current federal income taxes		435	344	76
Income tax expense		$ 229	$ 264	$ 300
Federal statutory income tax rate		21.00%	21.00%	21.00%
Deferred income tax expense		$ (246)	$ (140)	$ 224
Increase (Decrease) to deferred income tax expense				23
Increase (Decrease) in regulatory liabilities				31
Income tax benefit associated with remeasurement of state deferred taxes		0	0	0
Unrecognized tax benefits that would impact effective tax rate				2
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits			(2)	(2)
Virginia Electric and Power Company | Maximum
Income Taxes [Line Items]
Unrecognized tax benefits that would impact effective tax rate			1
SCANA
Income Taxes [Line Items]
Deferred income tax expense		194
Discontinued Operations
Income Taxes [Line Items]
Income tax expense		(204)	142	58
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits		5
Discontinued Operations | Maximum
Income Taxes [Line Items]
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits			(1)	(1)
Continuing Operations
Income Taxes [Line Items]
Increase (Decrease) in tax expense as a result of changes in unrecognized tax benefits		(6)	$ 3	$ 6
Cove Point
Income Taxes [Line Items]
Ownership interest percentage of limited partner interests			25.00%
Current federal income taxes			$ 362
Benefit for deferred income taxes			147
Federal tax credits			208
Atlantic Coast Pipeline | Discontinued Operations | Supply Header Project
Income Taxes [Line Items]
Income tax charge		81
Federal
Income Taxes [Line Items]
Deferred income tax expense			$ 48
State
Income Taxes [Line Items]
Income tax benefit associated with remeasurement of state deferred taxes		45
GT&S Transaction
Income Taxes [Line Items]
State deferred income tax expense (benefit)		18
GT&S Transaction | Discontinued Operations
Income Taxes [Line Items]
Income tax expense (benefit) on non-deductible goodwill written off		$ 236