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Summary of Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Foreign Currency Transactions      
Gain (loss) on revaluation of foreign currency transactions and monetary assets and liabilities $ (2) $ 2 $ 13
Cash and Cash Equivalents      
Maximum original maturity period of cash equivalent investments (in months) 3 months    
Outstanding checks that were reclassified from cash and cash equivalents to be included in accounts payable 58 40  
Restricted Cash      
Restricted cash   20  
Accounts Receivable      
Advance cash payments received from third parties to mitigate credit risk 186 197  
Net accounts receivable, maximum age of balances past their scheduled invoice date (in days) 30 days 30 days  
Allowance for doubtful accounts receivable 5 5  
Asset Retirement Obligations      
Fair value of asset retirement obligations 9 5  
Impairment of Long-Lived Assets      
Impairment charges - predominantly related to assets taken out of service 5 13  
Maximum
      
Impairment of Long-Lived Assets      
Impairment charges - predominantly related to assets taken out of service     $ 1