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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2011
Income Taxes [Line Items]          
Company's effective tax rate 27.00% 29.00% 28.00% 42.00%  
Liability for unrecognized tax benefits $ 41.0   $ 41.0   $ 45.0
Liability for unrecognized tax benefits that would impact the effective tax rate, if recognized 34.7   34.7    
Accrued interest on liability for unrecognized tax benefits 5.7   5.7   5.0
Expected decrease in unrecognized tax benefits within next 12 months $ 2.5   $ 2.5