Significant Accounting Policies (Checks the Outstanding Accounts Payable but not yet Presented for Payment and Recorded) (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounts Payable [Line Items]
Accounts payable for checks outstanding	$ 70	$ 50
Virginia Electric and Power Company
Accounts Payable [Line Items]
Accounts payable for checks outstanding	$ 15	$ 30