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Intangible Assets (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Intangible Assets (Textual)      
Gross carrying amount of intangible assets $ 429 $ 417  
Accumulated amortization of intangible assets (216) (190)  
Amortization expense of intangible assets 22 18 22
Future Amortization Expense      
Future amortization expense 2013 21    
Future amortization expense 2014 21    
Future amortization expense 2015 21    
Future amortization expense 2016 18    
Future amortization expense 2017 $ 7