Regulatory Matters - Schedule of Additional Significant Riders Associated with Virginia Power Projects (Parenthetical) (Detail) - Virginia Electric and Power Company $ in Millions	1 Months Ended					9 Months Ended
	Jun. 30, 2022 USD ($)	May 31, 2022 USD ($)	Dec. 31, 2021 USD ($) program	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)
Rider SNA
Public Utilities General Disclosures [Line Items]
Total revenue requirement						$ 107
Rider T1
Public Utilities General Disclosures [Line Items]
Total revenue requirement						706
Rider U
Public Utilities General Disclosures [Line Items]
Total revenue requirement						$ 95
Virginia Regulation | Previous Phase
Public Utilities General Disclosures [Line Items]
Projected capital investment	$ 74				$ 60
Virginia Regulation | Rider SNA | Operating Segments | Transmission Component Of Virginia Powers
Public Utilities General Disclosures [Line Items]
Projected capital investment				$ 1,200
Virginia Regulation | Rider T1 | Operating Segments
Public Utilities General Disclosures [Line Items]
Total revenue requirement		$ 224
Virginia Regulation | Rider T1 | Operating Segments | Transmission Component Of Virginia Powers
Public Utilities General Disclosures [Line Items]
Total revenue requirement		$ 482
Virginia Regulation | Rider U | Previous Phase
Public Utilities General Disclosures [Line Items]
Projected capital investment					$ 35
Virginia Regulation | Rider DSM
Public Utilities General Disclosures [Line Items]
Amount of cost cap recovery			$ 140
Public utilities energy efficiency program cost exceed percentage			15.00%
Virginia Regulation | Rider DSM | Operating Segments | Energy Efficiency Program
Public Utilities General Disclosures [Line Items]
Number of new energy efficiency programs | program			9