Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Detail) - 9 months ended Sep. 30, 2020		USD ($) MWh Bcf gal	EUR (€)
Fixed Price - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity	[1]	74
Fixed Price - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity	[1]	38
Basis - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity		240
Basis - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity		140
Fixed Price - Electricity - Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh		6,380,180
Fixed Price - Electricity - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh		73,133,287
Financial Transmission Rights - Electricity- Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh		73,133,287
Liquids - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | gal	[2]	11,004,000
Interest Rate - Current Derivative Contract
Derivative [Line Items]
Derivative payment | $	[3]	$ 1,600,000,000
Interest Rate - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Derivative payment | $	[3]	$ 0
Foreign Exchange - Current Derivative Contract
Derivative [Line Items]
Derivative payment | €	[3]		€ 250,000,000
Fixed Price - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity	[1]	13
Fixed Price - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity	[1]	0
Basis - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity		517
Basis - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity		498
Fixed Price - Electricity - Non-current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh		3,128,300
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
Liquids - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | gal	[2]	0
Interest Rate - Non-current Derivative Contract
Derivative [Line Items]
Derivative payment | $	[3]	$ 6,916,692,492
Interest Rate - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Derivative payment | $		$ 2,050,000,000
Foreign Exchange - Non- Current Derivative Contract
Derivative [Line Items]
Derivative payment | €	[3]		€ 0

[1] Includes options.

[2] Includes NGLs.

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