Employee Benefit Plans (Components of AOCI and Regulatory Assets and Liabilities) (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 194
Prior service (credit) cost	1
Pension Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	7
Prior service (credit) cost	0
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	5
Prior service (credit) cost	(50)
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	2
Prior service (credit) cost	$ (5)