Operating Segments - Virginia Power (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Charge for Expected customer credit reinvestment offset			$ 200
Charge for Expected customer credit reinvestment offset, net of tax			149
Gain loss on investments held in nuclear decommissioning trust funds, after tax	$ (36)	$ (94)	(223)	$ (77)
Virginia Electric and Power Company
Segment Reporting Information [Line Items]
Asset early retirement expense				369
Asset early retirement expense after tax				275
Gain loss on investments held in nuclear decommissioning trust funds, after tax	$ 5	$ (15)	(36)	(29)
Charge related to a voluntary retirement program				197
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
Operating Segments
Segment Reporting Information [Line Items]
After- tax net expenses			1,300	1,800
Gain loss on investments held in nuclear decommissioning trust funds				364
Gain loss on investments held in nuclear decommissioning trust funds, after tax				272
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net expenses			3,400	1,700
Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net expenses			815	653
Asset early retirement expense			751
Asset early retirement expense after tax			559
Charge for Expected customer credit reinvestment offset			200
Charge for Expected customer credit reinvestment offset, net of tax			149
Operating Segments | Virginia Electric and Power Company | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net expenses			$ 815	$ 673