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Organization and Basis of Presentation Equity Method Investees (Details) - USD ($)
$ in Millions
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 514 $ 434 $ 415
Gas Storage and Pipelines      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees 296 224  
Gas Storage and Pipelines | NEXUS Pipeline      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 89 $ 16  
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 $ 96 $ 98  
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 $ 111 $ 110  
Equity Method Investment, Ownership Percentage 26.00% 26.00%  
Other Segments      
Schedule of Equity Method Investments [Line Items]      
Investments in equity method investees $ 218 $ 210