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Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Dominion Energy Gas Holdings, LLC
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ 2	$ 2
Total realized and unrealized gains (losses):
Included in other comprehensive income (loss)		1	(3)
Transfers out of Level 3		1	3
Ending balance			2
Commodity
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 64	150	139
Total realized and unrealized gains (losses):
Included in other comprehensive income (loss)	0	1	(2)
Included in regulatory assets/liabilities	(90)	(44)	42
Settlements	17	(27)	6
Purchases	(10)	0	0
Sales	6	0	0
Transfers out of Level 3	(3)	1	3
Ending balance	(37)	64	150
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets still held at the reporting date	0	0	2
Commodity | Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	60	147	143
Total realized and unrealized gains (losses):
Included in regulatory assets/liabilities	(88)	(45)	40
Settlements	13	(25)	7
Ending balance	(37)	60	147
Operating Revenue | Commodity
Total realized and unrealized gains (losses):
Included in earnings	(1)	(2)	3
Electric fuel and other energy-related purchases | Commodity
Total realized and unrealized gains (losses):
Included in earnings	(22)	(15)	(42)
Electric fuel and other energy-related purchases | Commodity | Virginia Electric and Power Company
Total realized and unrealized gains (losses):
Included in earnings	(22)	(17)	(43)
Purchased Gas | Commodity
Total realized and unrealized gains (losses):
Included in earnings	$ 2	$ 0	$ 1

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Fair value, net derivative asset (liability) measured on recurring basis, unobservable inputs reconciliation, gain (loss) included in regulatory assets and liabilities.

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Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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Amount of gain (loss) recognized in other comprehensive income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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