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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Income Taxes [Line Items]        
Effective income tax rate 31.10% 31.70% 31.40% 31.90%
Reasonably possible decrease in total unrecognized tax benefits, minimum $ 3   $ 3  
Reasonably possible decrease in total unrecognized tax benefits, maximum $ 18   $ 18