Stock-Based Compensation - Stock Options Granted and Outstanding (Details) - $ / shares	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013	May. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of period (shares)	8,025,794	7,885,638	7,609,117
Granted (shares)	1,590,185	2,111,649	1,722,081
Canceled (shares)	(486,720)	(699,314)	(884,384)
Exercised (shares)	(1,293,689)	(1,272,179)	(561,176)
Outstanding, end of period (shares)	7,835,570	8,025,794	7,885,638
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, beginning of period, Weighted Average Exercise Price (dollars per share)	$ 43.12	$ 37.60	$ 36.04
Granted, Weighted Average Exercise Price (dollars per share)	84.59	61.04	44.67
Canceled, Weighted Average Exercise Price (dollars per share)	55.50	42.42	38.69
Exercised, Weighted Average Exercise Price (dollars per share)	38.11	39.03	36.44
Outstanding, end of period, Weighted Average Exercise Price (dollars per share)	$ 51.59	$ 43.12	$ 37.60
Number of exercisable options (shares)	1,426,550	1,583,413	1,815,795	2,105,702