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Goodwill and Intangible Assets (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Goodwill [Line Items]      
Amortization expense for intangible assets $ 73 $ 78 $ 71
Acquisition of intangible assets $ 124    
Weighted-average amortization period (years) 15 years    
Virginia Electric and Power Company      
Goodwill [Line Items]      
Amortization expense for intangible assets $ 29 25 24
Acquisition of intangible assets $ 40    
Weighted-average amortization period (years) 12 years    
Dominion Gas Holdings, LLC      
Goodwill [Line Items]      
Amortization expense for intangible assets $ 6 $ 18 $ 17
Acquisition of intangible assets $ 20    
Weighted-average amortization period (years) 12 years