Regulatory Matters - Schedule of Additional Significant Riders Associated with Virginia Power Projects (Parenthetical) (Detail) $ in Millions	1 Months Ended						12 Months Ended
	Dec. 31, 2021 USD ($) program	Oct. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)	May 31, 2021 USD ($)	Dec. 31, 2020 USD ($) program	Jun. 30, 2020 USD ($)	Dec. 31, 2021 USD ($)
Public Utilities General Disclosures [Line Items]
Number of new demand response programs | program					1
Rider SNA | Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Total revenue requirement							$ 109
Rider T1 | Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Total revenue requirement							874
Rider T1 | Virginia Regulation | Virginia Electric and Power Company | Operating Segments
Public Utilities General Disclosures [Line Items]
Total revenue requirement				$ 381
Rider T1 | Virginia Regulation | Virginia Electric and Power Company | Operating Segments | Transmission Component Of Virginia Powers
Public Utilities General Disclosures [Line Items]
Total revenue requirement				$ 493
Rider U | Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Total revenue requirement							$ 80
Rider U | Virginia Regulation | Virginia Electric and Power Company | Fifth Phase
Public Utilities General Disclosures [Line Items]
Projected capital investment						$ 36
Rider U | Virginia Regulation | Virginia Electric and Power Company | Previous Phase
Public Utilities General Disclosures [Line Items]
Projected capital investment			$ 61			$ 44
Rider U | Virginia Regulation | Virginia Electric and Power Company | Six Phase
Public Utilities General Disclosures [Line Items]
Projected capital investment			$ 35
Rider C4A | Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Amount of cost cap recovery	$ 140				$ 162
Nuclear Life Extension Program | Rider SNA | Virginia Regulation | Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Approved annual revenue required		$ 1,200
Energy Efficiency Program | Virginia Regulation | Virginia Electric and Power Company | Operating Segments
Public Utilities General Disclosures [Line Items]
Number of new energy efficiency programs | program	9
Period for cost cap					5 years
Energy Efficiency Program | Rider C4A | Virginia Regulation | Virginia Electric and Power Company | Operating Segments
Public Utilities General Disclosures [Line Items]
Number of new energy efficiency programs | program					10