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Summary of Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Foreign Currency Transactions      
Gain (loss) on revaluation of foreign currency transactions and monetary assets and liabilities $ (2) $ (2) $ 2
Cash and Cash Equivalents      
Maximum original maturity period of cash equivalent investments 3 months    
Outstanding checks that were reclassified from cash and cash equivalents to be included in accounts payable 72 58  
Accounts Receivable      
Advance cash payments received from third parties to mitigate credit risk 173 186  
Net accounts receivable, maximum age of balances past their scheduled invoice date 30 days 30 days  
Allowance for doubtful accounts receivable $ 4 $ 5