Share-Based Awards and Options - Stock Option Activity (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	0 Months Ended		3 Months Ended	9 Months Ended
	Feb. 28, 2015	May 31, 2014	Feb. 28, 2014	Feb. 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	530	766		766
Granted (in shares)			0	153
Forfeited (in shares)				(23)
Exercised (in shares)				(366)
Outstanding, end of period (in shares)				530
Options vested and exercisable (in shares)				392
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)	$ 49	$ 41		$ 41
Granted, weighted average exercise price (in dollars per share)				$ 72
Forfeited, weighted average exercise price (in dollars per share)				$ 56
Exercised, weighted average exercise price (in dollars per share)				$ 41
Options vested and exercisable, weighted average exercise price (in dollars per share)				$ 41
Outstanding, weighted average remaining contractual term	4 years 10 months 24 days	3 years 9 months 18 days
Options vested and exercisable, weighted average remaining contractual term	3 years 3 months 18 days
Outstanding, aggregate intrinsic value	$ 22.8	$ 21.3		$ 21.3
Options vested and exercisable, aggregate intrinsic value				$ 20.0