Significant Accounting Policies (Checks the Outstanding Accounts Payable but not yet Presented for Payment and Recorded) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts Payable [Line Items]
Accounts payable for checks outstanding	$ 29	$ 35
Virginia Electric and Power Company
Accounts Payable [Line Items]
Accounts payable for checks outstanding	9	16
Dominion Energy Gas Holdings, LLC
Accounts Payable [Line Items]
Accounts payable for checks outstanding	$ 6	$ 7