Operating Segments - Virginia Power (Narrative) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Gain (loss) on investments	$ 370	$ 101
Operating Segments
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(617)	(1,300)
Operating Segments | Nuclear Decommissioning Trust Funds
Segment Reporting Information [Line Items]
Gain (loss) on investments	309
Gain (loss) on investments, after tax	248
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(642)	(3,600)
After- tax net benefits (expenses) for specific items	(492)	(3,400)
Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(118)
Asset early retirement expense		751
Asset early retirement expense after tax		559
Benefit for change in expected CCRO reserve	130
Benefit for change in expected CCRO reserve, after tax	97
Charges associated with budget process related to customer arrears	77
Charges associated with budget process related to customer arrears, after tax	57
Charge associated with storm damage and service restoration	68
Charge associated with storm damage and service restoration, after tax	50
Loss from unbilled revenue reduction	151
Loss from unbilled revenue reduction, after tax	112
Net charge associated with proposed settlement of the 2021 Triennial Review	119
Net charge associated with proposed settlement of the 2021 Triennial Review, after tax	89
Charge for expected CCRO		200
Charge for expected CCRO, after tax		149
Operating Segments | Virginia Electric and Power Company | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(118)	(792)
After- tax net benefits (expenses) for specific items	$ (186)	$ (815)