Quarterly report pursuant to Section 13 or 15(d)

Income Taxes (Details)

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Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Feb. 29, 2012
Feb. 28, 2011
Feb. 29, 2012
Feb. 28, 2011
Aug. 31, 2011
Income Taxes [Abstract]          
Effective income tax rate 23.00% 21.80% 23.10% 21.10%  
Gross liability for unrecognized tax benefits, excluding interest and penalties $ 28.6   $ 28.6   $ 26.2
Liabilities for the payment of interest and penalties related to its unrecognized tax benefits $ 5.9   $ 5.9   $ 5.1