Operating Revenue (Schedule of Aggregate Amount of Transaction Price Allocated To Fixed-price Performance Obligations That Unsatisfied At End of Reporting Period And Expected To be Recognized) (Detail) $ in Millions	Sep. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-10-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 430
Revenue, expected to be recognized on multi-year contracts, period	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 1,672
Revenue, expected to be recognized on multi-year contracts, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 1,568
Revenue, expected to be recognized on multi-year contracts, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 1,454
Revenue, expected to be recognized on multi-year contracts, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 1,324
Revenue, expected to be recognized on multi-year contracts, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 13,799
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: (nil)
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	20,247
Virginia Electric and Power Company | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-10-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 5
Revenue, expected to be recognized on multi-year contracts, period	3 months
Virginia Electric and Power Company | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 21
Revenue, expected to be recognized on multi-year contracts, period	1 year
Virginia Electric and Power Company | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 3
Revenue, expected to be recognized on multi-year contracts, period	1 year
Virginia Electric and Power Company | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 1
Revenue, expected to be recognized on multi-year contracts, period	1 year
Virginia Electric and Power Company | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: (nil)
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 30
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-10-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 170
Revenue, expected to be recognized on multi-year contracts, period	3 months
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 633
Revenue, expected to be recognized on multi-year contracts, period	1 year
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 574
Revenue, expected to be recognized on multi-year contracts, period	1 year
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 489
Revenue, expected to be recognized on multi-year contracts, period	1 year
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 397
Revenue, expected to be recognized on multi-year contracts, period	1 year
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 2,171
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: (nil)
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 4,434