Regulatory Matters - Schedule of Additional Significant Riders Associated with Virginia Power Projects (Detail) - Virginia Electric and Power Company $ in Millions	9 Months Ended
	Sep. 30, 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
Rider BW
Public Utilities General Disclosures [Line Items]
Application Date	2020-10
Approval Date	July 2021
Rate Year Beginning	2021-09
Total Revenue Requirement (millions)	$ 113
Increase (decrease) in revenue requirement	$ 14
Rider US-2
Public Utilities General Disclosures [Line Items]
Application Date	2020-10
Approval Date	July 2021
Rate Year Beginning	2021-09
Total Revenue Requirement (millions)	$ 9
Rider E
Public Utilities General Disclosures [Line Items]
Application Date	2021-01
Approval Date	September 2021
Rate Year Beginning	2021-11
Total Revenue Requirement (millions)	$ 67
Increase (decrease) in revenue requirement	$ (18)
Rider B
Public Utilities General Disclosures [Line Items]
Application Date	2021-06
Approval Date	Pending
Rate Year Beginning	2022-04
Total Revenue Requirement (millions)	$ 16
Increase (decrease) in revenue requirement	$ (8)
Rider W
Public Utilities General Disclosures [Line Items]
Application Date	2021-06
Approval Date	Pending
Rate Year Beginning	2022-04
Total Revenue Requirement (millions)	$ 121
Increase (decrease) in revenue requirement	$ 1
Rider US-3
Public Utilities General Disclosures [Line Items]
Application Date	2021-08
Approval Date	Pending
Rate Year Beginning	2022-06
Total Revenue Requirement (millions)	$ 50
Increase (decrease) in revenue requirement	$ 12
Rider US-4
Public Utilities General Disclosures [Line Items]
Application Date	2021-08
Approval Date	Pending
Rate Year Beginning	2022-06
Total Revenue Requirement (millions)	$ 15
Increase (decrease) in revenue requirement	$ 5
Rider US-2
Public Utilities General Disclosures [Line Items]
Application Date	2021-10
Approval Date	Pending
Rate Year Beginning	2022-09
Total Revenue Requirement (millions)	$ 11
Increase (decrease) in revenue requirement	$ 2