Leases (Lease Assets and Liabilities Recorded in Consolidated Balance Sheets) (Parenthetical) (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Lessee Lease Disclosure [Line Items]
Finance lease assets, accumulated amortization	$ 39
Virginia Electric and Power Company
Lessee Lease Disclosure [Line Items]
Finance lease assets, accumulated amortization	3
Dominion Energy Gas Holdings, LLC
Lessee Lease Disclosure [Line Items]
Finance lease assets, accumulated amortization	$ 2