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Property Plant and Equipment (Narrative) (Detail)
$ in Millions
1 Months Ended 3 Months Ended
Mar. 31, 2018
USD ($)
a
field
Feb. 28, 2018
USD ($)
Jan. 31, 2018
a
Mar. 31, 2018
USD ($)
a
field
Mar. 31, 2017
USD ($)
Nov. 30, 2014
a
field
Virginia Electric and Power Company | Assignment of Tower Rental Portfolio | Disposal Group, Disposed of by Sale, Not Discontinued Operations            
Property Plant And Equipment [Line Items]            
Amount of consideration         $ 91  
Amount recognized in operating revenue and other income from sale       $ 2 $ 7  
Amount to be recognized in other income ratably through 2023 $ 33     33    
Dominion Energy Gas Holdings, LLC | Marcellus Shale | Oil and Gas Properties            
Property Plant And Equipment [Line Items]            
Amount of consideration   $ 28        
Development rights (number of acres) | a     18,000     24,000
Number of natural gas storage fields | field           1
Gas and oil area developed net remaining interest conveyed percentage     50.00%      
Dominion Energy Gas Holdings, LLC | Marcellus Shale | Oil and Gas Properties | Other operations and maintenance            
Property Plant And Equipment [Line Items]            
Gain from sale   28        
After tax gain on sale   $ 20        
Dominion Energy Gas Holdings, LLC | Uticaand Point Pleasant Shale | Oil and Gas Properties            
Property Plant And Equipment [Line Items]            
Amount of consideration $ 16     $ 16    
Development rights (number of acres) | a 11,000     11,000    
Number of natural gas storage fields | field 1     1    
Proceeds from assignment of Shale Development Rights $ 16          
Dominion Energy Gas Holdings, LLC | Uticaand Point Pleasant Shale | Oil and Gas Properties | Other operations and maintenance            
Property Plant And Equipment [Line Items]            
Gain from sale 16          
After tax gain on sale $ 12