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Acquisitions and Dispositions (Details 2) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dispositions      
Proceeds from sale of various property and equipment $ 22 $ 12 $ 3
Gain (loss) on sale of various property and equipment 6 (6)  
Maximum
     
Dispositions      
Gain (loss) on sale of various property and equipment     $ 1