Regulatory Matters - Summary of Virginia Power Electric Transmission Project Applied (Detail) - Virginia Electric and Power Company $ in Millions	9 Months Ended
	Sep. 30, 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
Rebuild and operate two lines in Chesterfield County, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2020-01
Approval Date	2020-06
Capacity of transmission line (kV) | kV	230
Length of kV line (miles | mi	3
The total estimated capital investment | $	$ 15
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	Pending
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
Approval Date	Pending
Capacity of transmission line (kV) | kV	230
The total estimated capital investment | $	$ 30
Rebuild and Install New Line in Counties of New Kent, King William, King and Queen Essex and Richmond, Virginia
Public Utilities General Disclosures [Line Items]
Application Date	2020-10
Approval Date	Pending
Capacity of transmission line (kV) | kV	230
Length of kV line (miles | mi	41
The total estimated capital investment | $	$ 100