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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Income Taxes [Line Items]        
Effective income tax rate 32.80% 33.40% 34.00% 31.50%
Minimum [Member]        
Income Taxes [Line Items]        
Reasonably possible decrease in unrecognized tax benefits $ 3   $ 3  
Maximum [Member]        
Income Taxes [Line Items]        
Reasonably possible decrease in unrecognized tax benefits $ 7   $ 7