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Asset Retirement Obligations (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Asset Retirement Obligation [Line Items]          
Asset Retirement Obligation Accretion Expense From Discontinued Operations Included in Asset Retirement Obligation Balance At End of Period $ 0 $ 0 $ 0 $ 1  
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]          
Beginning asset retirement obligations 193 191 194 198  
Asset Retirement Obligation, Liabilities Incurred 1 1 3 3  
Changes in estimates 2 0 3 (6)  
Disposition of wells (5) 0 (7) (4)  
Liabilities settled (6) (4) (14) (10)  
Accretion of discount from continuing operations 3 3 9 9  
Ending asset retirement obligations 188 191 188 191  
Asset retirement obligations, current portions 27   27   19
Discontinued Operations [Member]
         
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]          
Accretion of discount from continuing operations $ 0 $ 0 $ 1 $ 1