Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014
Basic Earnings per Share:
Net income	$ 64.5	$ 43.8	$ 162.0	$ 121.0
Less: Income attributable to participating securities	(0.2)	(0.4)	(0.7)	(1.2)
Net income available to common shareholders	$ 64.3	$ 43.4	$ 161.3	$ 119.8
Basic weighted average shares outstanding (in shares)	43.2	42.8	43.1	42.7
Basic earnings per share (in dollars per share)	$ 1.49	$ 1.01	$ 3.74	$ 2.81
Diluted Earnings per Share:
Net Income	$ 64.5	$ 43.8	$ 162.0	$ 121.0
Less: Income attributable to participating securities	(0.2)	(0.4)	(0.7)	(1.2)
Net income available to common shareholders	$ 64.3	$ 43.4	$ 161.3	$ 119.8
Basic weighted average shares outstanding (in shares)	43.2	42.8	43.1	42.7
Common stock equivalents	0.3	0.3	0.3	0.3
Diluted weighted average shares outstanding (in shares)	43.5	43.1	43.4	43.0
Diluted earnings per share (in dollars per share)	$ 1.48	$ 1.01	$ 3.72	$ 2.79