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Investments (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 9 Months Ended
Oct. 31, 2016
May 31, 2016
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]              
Contributions to equity method affiliates         $ 343 $ 124  
Investment in equity method affiliates     $ 1,895   1,895   $ 1,561 [1]
Dominion Energy Gas Holdings, LLC              
Schedule Of Equity Method Investments [Line Items]              
Equity in earnings on investments     4 $ 5 15 14  
Atlantic Coast Pipeline              
Schedule Of Equity Method Investments [Line Items]              
Additional membership percentage interest purchased 3.00%            
Contributions to equity method affiliates $ 14   $ 84 $ 74 $ 286 143  
Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline | Distribution              
Schedule Of Equity Method Investments [Line Items]              
Ownership interest (percentage)     48.00%   48.00%    
Atlantic Coast Pipeline | Pipelines | Duke Energy | Jointly Owned Natural Gas Pipeline | Distribution              
Schedule Of Equity Method Investments [Line Items]              
Ownership interest (percentage)     47.00%   47.00%    
Iroquois | Dominion Energy Gas Holdings, LLC | Partnership Interest              
Schedule Of Equity Method Investments [Line Items]              
Equity in earnings on investments         $ 15 14  
Distributions received from investment         17 $ 17  
Investment in equity method affiliates     $ 96   96   98
Carrying amount of investment that exceeded share of underlying equity     8   8    
Iroquois | Dominion Energy Gas Holdings, LLC | Partnership Interest | Other Income              
Schedule Of Equity Method Investments [Line Items]              
Percentage of non-controlling partnership interest sold   0.65%          
Sales price of non-controlling partnership interest   $ 7          
Amount of gain from sale   5          
Amount of after tax gain from sale   $ 3          
Categories of Investments, Marketable Securities, Trading Securities              
Schedule Of Equity Method Investments [Line Items]              
Rabbi trust securities     $ 109   $ 109   $ 104
[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.