Regulatory Matters - Summary of Additional Significant Riders Associated with Various Virginia Power Projects (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Increase (decrease) in revenue requirement	$ 11
Rider S | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Rate Year Beginning		2020-04
Total Revenue Requirement (millions)		$ 195,000,000
Increase (decrease) in revenue requirement		$ (20,000,000)
Rider GV | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-05
Approval Date		February 2020
Rate Year Beginning		2020-04
Total Revenue Requirement (millions)		$ 132,000,000
Increase (decrease) in revenue requirement		$ 12,000,000
Rider W | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-05
Approval Date		February 2020
Rate Year Beginning		2020-04
Total Revenue Requirement (millions)		$ 106,000,000
Increase (decrease) in revenue requirement		$ 1,000,000
Rider R | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-05
Approval Date		February 2020
Rate Year Beginning		2020-04
Total Revenue Requirement (millions)		$ 44,000,000
Increase (decrease) in revenue requirement		$ (13,000,000)
Rider B | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-05
Approval Date		February 2020
Rate Year Beginning		2020-04
Total Revenue Requirement (millions)		$ 32,000,000
Increase (decrease) in revenue requirement		$ (6,000,000)
Rider US-3 | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-07
Approval Date		Pending
Rate Year Beginning		2020-06
Total Revenue Requirement (millions)		$ 31,000,000
Increase (decrease) in revenue requirement		$ 21,000,000
Rider BW | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-10
Approval Date		Pending
Rate Year Beginning		2020-09
Total Revenue Requirement (millions)		$ 120,000,000
Increase (decrease) in revenue requirement		$ 1,000,000
Rider US-2 | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2019-10
Approval Date		Pending
Rate Year Beginning		2020-09
Total Revenue Requirement (millions)		$ 10,000,000
Increase (decrease) in revenue requirement		$ (5,000,000)
Rider E | Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Application Date		2020-01
Approval Date		Pending
Rate Year Beginning		2020-11
Total Revenue Requirement (millions)		$ 88,000,000
Increase (decrease) in revenue requirement		$ (16,000,000)