Share-Based Awards and Options - Stock Option Activity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Aug. 31, 2014	Aug. 31, 2013	May 31, 2014	Aug. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	766,000
Granted (in shares)	153,000	153,000
Forfeited (in shares)	(7,000)
Exercised (in shares)	(280,000)
Outstanding, end of period (in shares)	632,000		766,000
Options vested and exercisable (in shares)	473,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding, Weighted Average Exercise Price, beginning of period (in dollars per share)	$ 41
Granted, Weighted Average Exercise Price (in dollars per share)	$ 72
Forfeited, Weighted Average Exercise Price (in dollars per share)	$ 23
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 41
Outstanding, Weighted Average Exercise Price, end of period (in dollars per share)	$ 48		$ 41
Options vested and exercisable, Weighted Average Exercise Price (in dollars per share)	$ 41
Outstanding, Weighted Average Remaining Contractual Term	5 years 2 months 12 days		3 years 9 months 18 days
Options vested and exercisable, Weighted Average Remaining Contractual Term	3 years 8 months 12 days
Outstanding, Aggregate Intrinsic Value	$ 21.3			$ 15.5
Options vested and exercisable, Aggregate Intrinsic Value	$ 15.2