Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Detail)	3 Months Ended
	Mar. 31, 2021 USD ($) MWh Bcf
Fixed Price - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	60	[1]
Fixed Price - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	35	[1]
Basis - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	202
Basis - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	151
Fixed Price - Electricity - Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	10,745,307
Fixed Price - Electricity - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	3,770,002
Financial Transmission Rights - Electricity- Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	18,264,727
Financial Transmission Rights - Electricity- Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	18,264,727
Interest Rate - Current Derivative Contract
Derivative [Line Items]
Derivative payment | $	$ 1,250,000,000	[2]
Interest Rate - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Derivative payment | $	$ 850,000,000	[2]
Fixed Price - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	19	[1]
Fixed Price - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	18	[1]
Basis - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	496
Basis - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	495
Fixed Price - Electricity - Non-current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	9,789,934
Fixed Price - Electricity - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	3,029,859
Financial Transmission Rights - Electricity- Non-current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	0
Financial Transmission Rights - Electricity- Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	0
Interest Rate - Non-current Derivative Contract
Derivative [Line Items]
Derivative payment | $	$ 5,407,000,000	[2]
Interest Rate - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Derivative payment | $	$ 1,200,000,000	[2]

[1] Includes options.

[2] Maturity is determined based on final settlement period.