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Acquisitions, Divestitures, and Assets Held for Sale - Property Exchange (Details) - USD ($)
$ in Millions
12 Months Ended
Mar. 17, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Sep. 30, 2017
Nonmonetary Transaction [Line Items]          
Cash payment to acquire a third party's interest in the DBJV system   $ 5,031 $ 3,505 $ 6,067  
Delaware Basin Joint Venture System [Member]          
Nonmonetary Transaction [Line Items]          
Third party nonoperated interest percentage to be acquired 50.00%        
Delaware Basin Joint Venture System [Member] | Western Gas Partners, LP [Member]          
Nonmonetary Transaction [Line Items]          
Cash payment to acquire a third party's interest in the DBJV system $ 155        
Gain on property exchange $ 126        
Operated Interest         100.00%
Marcellus Assets [Member] | Western Gas Partners, LP [Member]          
Nonmonetary Transaction [Line Items]          
Non operated interest percentage 33.75%