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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
3 Months Ended
Mar. 31, 2018
USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-04-01  
Revenues From Contract With Customer [Line Items]  
Revenue, expected to be recognized on multi-year contracts $ 1,251
Revenue, expected to be recognized on multi-year contracts, period 9 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 $ 1,709
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 $ 1,593
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 $ 1,474
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 $ 1,327
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 $ 14,686
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 22,040
Virginia Electric and Power Company | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-04-01  
Revenues From Contract With Customer [Line Items]  
Revenue, expected to be recognized on multi-year contracts $ 16
Revenue, expected to be recognized on multi-year contracts, period 9 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 $ 41
Dominion Energy Gas Holdings, LLC | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-04-01  
Revenues From Contract With Customer [Line Items]  
Revenue, expected to be recognized on multi-year contracts $ 479
Revenue, expected to be recognized on multi-year contracts, period 9 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 $ 632
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 $ 562
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 $ 473
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 $ 379
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 $ 2,084
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 $ 4,609