Operating Segments - Virginia Power (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Gain loss on investments held in nuclear decommissioning trust funds, after tax	$ 38	$ 48	$ (187)	$ 17
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	$ (9)	(41)	(14)
Charge related to a voluntary retirement program				192
Charge related to a voluntary retirement program, after-tax				143
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			2,900	1,800
Gain loss on investments held in nuclear decommissioning trust funds			145	336
Gain loss on investments held in nuclear decommissioning trust funds, after tax			115	251
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net expenses			3,100	2,100
Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net expenses			654	607
Asset early retirement expense			751
Asset early retirement expense after tax			559
Operating Segments | Virginia Electric and Power Company | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net expenses			$ 654	$ 652