Regulatory Matters - Schedule of Additional Significant Riders Associated with Virginia Power Projects (Detail) - Virginia Electric and Power Company $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($)
Rider B
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	February 2021
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 24
Increase (decrease) in revenue requirement	$ (8)
Rider GV
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	February 2021
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 153
Increase (decrease) in revenue requirement	$ 21
Rider R
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	February 2021
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 58
Increase (decrease) in revenue requirement	$ 14
Rider S
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	February 2021
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 194
Increase (decrease) in revenue requirement	$ (1)
Rider W
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	February 2021
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 120
Increase (decrease) in revenue requirement	$ 14
Rider US-3
Public Utilities General Disclosures [Line Items]
Application Date	2020-07
Approval Date	March 2021
Rate Year Beginning	2021-06
Total Revenue Requirement (millions)	$ 38
Increase (decrease) in revenue requirement	$ 10
Rider US-4
Public Utilities General Disclosures [Line Items]
Application Date	2020-07
Approval Date	March 2021
Rate Year Beginning	2021-06
Total Revenue Requirement (millions)	$ 10
Increase (decrease) in revenue requirement	$ 3