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Asset Retirement Obligations (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]          
Beginning asset retirement obligations $ 297 $ 285 $ 297 $ 285  
Asset Retirement Obligation, Liabilities Incurred 1 0 1 0  
Changes in estimates 7 0 7 0  
Disposition of wells (7) 0 (7) 0  
Liabilities settled (9) (9) (14) (13)  
Accretion of discount from continuing operations 5 5 10 9  
Ending asset retirement obligations 294 $ 281 294 $ 281  
Asset retirement obligations, current portions $ 46   $ 46   $ 39