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Asset Retirement Obligations (Summary Of Changes In Asset Retirement Obligations) (Details) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Asset Retirement Obligations [Abstract]      
Asset retirement obligations as of beginning of period $ 2,228 $ 2,095  
Liabilities incurred 79 88  
Liabilities settled (38) (46)  
Revision of estimated obligation 75 104  
Liabilities assumed by others (949) (15)  
Accretion expense on discounted obligation 70 86  
Foreign currency translation adjustment (55) (44)  
Asset retirement obligations as of end of period 1,410 2,268  
Less current portion 62 107  
Asset retirement obligations, long-term $ 1,348 $ 2,161 $ 2,140