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Asset Retirement Obligations (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]          
Beginning asset retirement obligations $ 188 $ 194 $ 189 $ 194  
Asset Retirement Obligation, Liabilities Incurred 0 1 1 2  
Changes in estimates 0 0 0 1  
Disposition of wells 0 0 0 (1)  
Liabilities settled (4) (5) (9) (9)  
Accretion of discount from continuing operations 3 3 6 6  
Ending asset retirement obligations 187 $ 193 187 $ 193  
Asset retirement obligations, current portions $ 33   $ 33   $ 28