Operating Segments - Virginia Power (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Gain loss on investments	$ 152	$ (526)
Operating Segments
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(87)	(1,000)
Operating Segments | Nuclear Decommissioning Trust Funds
Segment Reporting Information [Line Items]
Gain loss on investments	134	(538)
Gain loss on investments, net of tax	100	(410)
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	71	(1,100)
After- tax net benefits (expenses) for specific items	115	(1,100)
Operating Segments | Virginia Electric and Power Company
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(58)
Asset early retirement expense		754
Asset early retirement expense after tax		561
Benefit for change in CCRO reserve	130
Benefit for change in CCRO reserve, net of tax	97
Charges associated with budget process related to customer arrears	76
Charges associated with budget process related to customer arrears, net of tax	56
Charge associated with storm damage and service restoration	51
Charge associated with storm damage and service restoration, after tax	38
Loss from unbilled revenue reduction	151
Loss from unbilled revenue reduction, net of tax	112
Operating Segments | Virginia Electric and Power Company | Nuclear Decommissioning Trust Funds
Segment Reporting Information [Line Items]
Gain loss on investments		(62)
Gain loss on investments, net of tax		(46)
Operating Segments | Virginia Electric and Power Company | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net benefits (expenses)	(58)	(707)
After- tax net benefits (expenses) for specific items	$ (117)	$ (634)