Regulatory Matters - Summary of Virginia Power Electric Transmission Project Applied (Detail) - Virginia Electric and Power Company $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) kV mi
Rebuild and operate five segments between the Loudoun and Ox substations
Public Utilities General Disclosures [Line Items]
Application Date	2019-08
Approval Date	2020-06
Capacity of transmission line (kV) | kV	230
Length of kV line (miles) | mi	19
The total estimated capital investment | $	$ 70
Build new Lockridge substation and line loop in Loudoun County, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2019-12
Approval Date	2020-10
Capacity of transmission line (kV) | kV	230
The total estimated capital investment | $	$ 35
Bristers-Ladysmith Rebuild Project in the counties of Fauquier, Stafford, Spotsylvania, and Caroline, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2020-05
Approval Date	2021-02
Capacity of transmission line (kV) | kV	500
Length of kV line (miles) | mi	37
The total estimated capital investment | $	$ 110
Relocate and replace a transmission line underground between the Tysons substation and the future Spring Hill substation
Public Utilities General Disclosures [Line Items]
Application Date	2020-09
Capacity of transmission line (kV) | kV	230
The total estimated capital investment | $	$ 30
Approval Date	Pending
Rebuild an Existing Transmission Line and Install New Line Adjacent thereto in Counties of New Kent, King William, King and Queen Essex and Richmond, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2020-10
Capacity of transmission line (kV) | kV	230
Length of kV line (miles) | mi	41
The total estimated capital investment | $	$ 100
Approval Date	Pending
Rebuild Clubhouse - Dry Bread Line and Dry Bread Lakeview Line in Greensville County, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2020-11
Capacity of transmission line (kV) | kV	230
Length of kV line (miles) | mi	13
The total estimated capital investment | $	$ 20
Approval Date	Pending
Rebuild transmission lines and related projects in the Counties of York and James City and the City of Williamsburg, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2021-01
Capacity of transmission line (kV) | kV	230
Length of kV line (miles) | mi	11
The total estimated capital investment | $	$ 30
Approval Date	Pending