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Asset Retirement Obligations (Details) (USD $)
In Millions
3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Dec. 31, 2010
Asset Retirement Obligations          
Asset retirement obligations as of beginning of period     $ 1,497 $ 1,513  
Liabilities incurred     23 25  
Liabilities settled     (39) (71)  
Revision of estimated obligation     16 194  
Liabilities assumed by others       (256)  
Accretion expense on discounted obligation 23 24 46 50  
Foreign currency translation adjustment     28 (14)  
Asset retirement obligations as of end of period 1,571 1,441 1,571 1,441  
Less current portion 72 95 72 95  
Asset retirement obligations, long-term $ 1,499 $ 1,346 $ 1,499 $ 1,346 $ 1,423