Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Detail) - 9 months ended Sep. 30, 2018		USD ($) MWh Bcf gal	EUR (€)
Fixed Price - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity	[1]	71
Fixed Price - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity	[1]	24
Fixed Price - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity	[1]	29
Fixed Price - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity	[1]	4
Basis - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity		261
Basis - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity		161
Basis - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity		607
Basis - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity		521
Fixed Price - Electricity - Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	[1]	9,770,320
Fixed Price - Electricity - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	[1]	660,190
Fixed Price - Electricity - Non-current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	[1]	957,820
Financial Transmission Rights - Electricity- Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh		74,350,989
Financial Transmission Rights - Electricity- Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh		73,336,004
Liquids - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | gal	[2]	35,084,400
Liquids - Current Derivative Contract | Dominion Energy Gas Holdings, LLC
Derivative [Line Items]
Volume of derivative activity | gal		29,708,400
Foreign currency
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | €			€ 250,000,000
Foreign currency | Dominion Energy Gas Holdings, LLC
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | €			€ 250,000,000
Foreign Exchange - Non- Current Derivative Contract
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[3],[4]	$ 280,000,000
Foreign Exchange - Non- Current Derivative Contract | Dominion Energy Gas Holdings, LLC
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[3],[5]	280,000,000
Interest Rate - Current Derivative Contract
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[4]	600,000,000
Interest Rate - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[4]	600,000,000
Interest Rate - Non-current Derivative Contract
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[4]	5,023,819,541
Interest Rate - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[4]	1,000,000,000
Interest Rate - Non-current Derivative Contract | Dominion Energy Gas Holdings, LLC
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros) | $	[5]	$ 1,050,000,000

[1] Includes options.

[2] Includes NGLs and oil.

[3] Euro equivalent volumes are €250,000,000.

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

[5] Maturity is based on final settlement period.