Operating Segments - Virginia Power (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Charge for expected CCRO, net of tax		$ 149
Charges associated with legislation enacted related to customer arrears, net of tax	$ 94
Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Charge for expected CCRO, net of tax		$ 149
Charges associated with legislation enacted related to customer arrears, net of tax	$ 94
Operating Segments
Segment Reporting Information [Line Items]
After- tax net expenses			$ 1,200	$ 1,900	$ 196
Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net expenses			863
Asset early retirement expense			751	346
Asset early retirement expense after tax			559	257
Charge for expected CCRO			130
Charge for expected CCRO, net of tax			97
Charges associated with legislation enacted related to customer arrears			127
Charges associated with legislation enacted related to customer arrears, net of tax			94
Charge related to a voluntary retirement program				198
Charge related to a voluntary retirement program, after-tax				146
Asset planned early retirement expense				160
Asset planned early retirement expense, after tax				119
Operating revenue recorded charge				135
Operating revenue recorded charge, after tax				100
Cancellation abandonment expense				62
Cancellation abandonment expense, after tax				46
Benefit from revision of future closure costs				113
Benefit from revision of future closure costs, after tax				84
One-time rate credit amount					215
One-time rate credit amount after tax					160
Charge associated with major storm damage and service restoration					70
Charge associated with major storm damage and service restoration, after tax					52
Operating Segments | Virginia Electric and Power Company | Virginia Regulation
Segment Reporting Information [Line Items]
Charge associated with asset retirement obligations for ash ponds and landfills at certain utility generation facilities					81
Environmental remediation expense net of tax					60
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net expenses			3,700	1,800	(117)
After- tax net expenses for specific items			3,400	1,500	(322)
Operating Segments | Corporate and Other | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net expenses			863	634	312
After- tax net expenses for specific items			$ 915	$ 627	$ 312