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, 2020 USD ($)
Rider US-3
Public Utilities General Disclosures [Line Items]
Application Date	2019-07
Approval Date	March 2020
Rate Year Beginning	2020-06
Total Revenue Requirement (millions)	$ 28
Increase (decrease) in revenue requirement	$ 18
Rider BW
Public Utilities General Disclosures [Line Items]
Application Date	2019-10
Approval Date	June 2020
Rate Year Beginning	2020-09
Total Revenue Requirement (millions)	$ 99
Increase (decrease) in revenue requirement	$ (20)
Rider B
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	Pending
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	Pending
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 154
Increase (decrease) in revenue requirement	$ 22
Rider US-2
Public Utilities General Disclosures [Line Items]
Application Date	2019-10
Approval Date	July 2020
Rate Year Beginning	2020-09
Total Revenue Requirement (millions)	$ 10
Increase (decrease) in revenue requirement	$ (5)
Rider R
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	Pending
Rate Year Beginning	2021-04
Total Revenue Requirement (millions)	$ 59
Increase (decrease) in revenue requirement	$ 15
Rider E
Public Utilities General Disclosures [Line Items]
Application Date	2020-01
Approval Date	September 2020
Rate Year Beginning	2020-11
Total Revenue Requirement (millions)	$ 85
Increase (decrease) in revenue requirement	$ (19)
Rider S
Public Utilities General Disclosures [Line Items]
Application Date	2020-06
Approval Date	Pending
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	Pending
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	Pending
Rate Year Beginning	2021-06
Total Revenue Requirement (millions)	$ 39
Increase (decrease) in revenue requirement	$ 10
Rider US-4
Public Utilities General Disclosures [Line Items]
Application Date	2020-07
Approval Date	Pending
Rate Year Beginning	2021-06
Total Revenue Requirement (millions)	$ 12
Increase (decrease) in revenue requirement	$ 4
Rider BW
Public Utilities General Disclosures [Line Items]
Application Date	2020-10
Approval Date	Pending
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	Pending
Rate Year Beginning	2021-09
Total Revenue Requirement (millions)	$ 10
Increase (decrease) in revenue requirement	$ 0

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