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Investments in Unconsolidated Affiliates (Narrative) (Details) - USD ($)
$ in Millions
2 Months Ended 12 Months Ended
Dec. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Oct. 31, 2016
Oct. 03, 2016
Investments In Unconsolidated Affiliates [Line Items]            
Distributions from equity investments   $ 108 $ 13 $ 31    
Distributions from equity investments, return of capital   137 281 1    
Income (Loss) from Equity Method Investments   83 119 (15)    
Asset Impairment Charges   402 282 18    
Atlantic Coast Pipeline [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Distributions from equity investments, return of capital   265        
Electric Utilities and Infrastructure [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Income (Loss) from Equity Method Investments   $ 6 5 5    
Electric Utilities and Infrastructure [Member] | Duke American Transmission Co. [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity method investment, ownership percentage   50.00%        
Electric Utilities and Infrastructure [Member] | Pioneer Transmission [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity method investment, ownership percentage   50.00%        
Gas Utilities and Infrastructure [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Income (Loss) from Equity Method Investments   $ 27 62 19    
Gas Utilities and Infrastructure [Member] | Atlantic Coast Pipeline [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity method investment, ownership percentage   47.00%        
Gas Utilities and Infrastructure [Member] | Constitution Pipeline [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity method investment, ownership percentage   24.00%        
Commercial Renewables [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Income (Loss) from Equity Method Investments   $ (1) (5) (82)    
Asset Impairment Charges       71    
Commercial Renewables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Asset Impairment Charges       71    
Commercial Renewables [Member] | DS Cornerstone [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity method investment, ownership percentage   50.00%        
Other [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Income (Loss) from Equity Method Investments   $ 51 $ 57 $ 43    
Other [Member] | National Methanol Company [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity method investment, ownership percentage   17.50% 25.00%      
Board representation and voting rights, ownership percentage   25.00%        
Piedmont Natural Gas [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Distributions from equity investments $ 1 $ 1 $ 4   $ 26  
Distributions from equity investments, return of capital 1 3 2   18  
Income (Loss) from Equity Method Investments $ 2 $ 7 (6)   29  
Asset Impairment Charges     $ 7      
Piedmont Natural Gas [Member] | SouthStar [Member]            
Investments In Unconsolidated Affiliates [Line Items]            
Equity Method Investment Ownership Percentage Sold           15.00%
Proceeds from Sale of Equity Method Investments         160  
Gain on Sale of Investments         81  
Income (Loss) from Equity Method Investments         $ 19