Quarterly report pursuant to Section 13 or 15(d)

Income Taxes - Additional Information (Detail)

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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
May 31, 2012
May 31, 2011
May 31, 2012
May 31, 2011
Aug. 31, 2011
Income Taxes [Line Items]          
Effective income tax rate 16.10% 23.00% 20.90% 22.00%  
Gross liability for unrecognized tax benefits, excluding interest and penalties $ 24.2   $ 24.2   $ 26.2
Liabilities for payment of interest and penalties related to its unrecognized tax benefits $ 4.4   $ 4.4   $ 5.1