Regulatory Matters - Schedule of Additional Significant Riders Associated with Virginia Power Projects (Detail) - Virginia Electric and Power Company - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2020
Public Utilities General Disclosures [Line Items]
Increase (Decrease) Over Previous Year	$ 14
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) Over Previous Year		$ 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) Over Previous Year		$ (20)
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) Over Previous Year		$ (5)
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) Over Previous Year		$ (19)
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) Over Previous Year		$ (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) Over Previous Year		$ 22
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) Over Previous Year		$ 15
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) Over Previous Year		$ (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) Over Previous Year		$ 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) Over Previous Year		$ 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) Over Previous Year		$ 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) Over Previous Year		$ 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
Rider E
Public Utilities General Disclosures [Line Items]
Application Date		2021-01
Approval Date		Pending
Rate Year Beginning		2021-11
Total Revenue Requirement (millions)		$ 67
Increase (Decrease) Over Previous Year		$ (18)