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Organization and Basis of Presentation (Equity Method Investees) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 752 $ 514 $ 434
Gas Storage and Pipelines      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees 538 296  
Gas Storage and Pipelines | NEXUS Pipeline      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 322 $ 89  
Equity method investment, ownership percentage 50.00% 50.00%  
Gas Storage and Pipelines | Vector Pipeline      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 100 $ 96  
Equity method investment, ownership percentage 40.00% 40.00%  
Gas Storage and Pipelines | Millennium Pipeline      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 116 $ 111  
Equity method investment, ownership percentage 26.00% 26.00%  
Other Segments      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 214 $ 218