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Property, Plant and Equipment - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Property, Plant and Equipment [Line Items]      
Net Cost of Assets under capital leases $ 3 $ 7  
Depreciation charge 930 1,068 1,033
Capital investment funding 1 11 4
Reduction in depreciation charges due to public funding 10 12 13
Cash proceeds from sale of equipment $ 16 $ 26 $ 29