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Goodwill Goodwill (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Sep. 01, 2016
Goodwill [Line Items]      
Goodwill, Written off Related to Sale of Business Unit $ 3 $ 1,644  
Natural Gas Pipelines Regulated      
Goodwill [Line Items]      
Goodwill, Written off Related to Sale of Business Unit 0 1,635  
Terminals      
Goodwill [Line Items]      
Goodwill, Written off Related to Sale of Business Unit 3 9  
Products Pipelines Terminals      
Goodwill [Line Items]      
Goodwill, Written off Related to Sale of Business Unit 0 0  
CO2      
Goodwill [Line Items]      
Goodwill, Written off Related to Sale of Business Unit $ 0 0  
Sale Equity Interest in SNG [Member]      
Goodwill [Line Items]      
Goodwill, Written off Related to Sale of Business Unit   $ 1,635  
Disposal Group, Equity Interest Sold     50.00%