Stock-Based Compensation - Restricted Stock Awards Granted and Outstanding (Details) - Restricted Stock Awards - $ / shares	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding, beginning of period (shares)	2,210,113	2,158,778	2,015,023
Granted (shares)	1,069,748	627,033	661,514
Canceled (shares)	(70,998)	(50,277)	(52,124)
Vested (shares)	(605,427)	(525,421)	(465,635)
Outstanding, end of period (shares)	2,603,436	2,210,113	2,158,778
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, Weighted Average Grant Price, beginning of period (dollars per share)	$ 57.60	$ 45.04	$ 35.97
Granted, Weighted Average Grant Price (dollars per share)	92.10	80.73	60.66
Canceled, Weighted Average Grant Price (dollars per share)	65.79	49.33	37.95
Vested, Weighted Average Grant Price (dollars per share)	38.76	34.39	28.76
Outstanding, Weighted Average Grant Price, end of period (dollars per share)	$ 75.94	$ 57.60	$ 45.04