Earnings per Share - Summary of Buyback Activity by Program (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Purchase Price	$ 551,970	$ 370,599	$ 215,681
Share Repurchase Programs
Equity, Class of Treasury Stock [Line Items]
Shares	6,851	6,665
Avg. Price per Share	$ 78.47	$ 54.31
Purchase Price	$ 537,572	$ 361,960
October 18, 2011
Equity, Class of Treasury Stock [Line Items]
Shares	0	3,324
Avg. Price per Share	$ 0.00	$ 48.87
Purchase Price	$ 0	$ 162,460
July 30, 2013
Equity, Class of Treasury Stock [Line Items]
Shares	3,981	3,341
Avg. Price per Share	$ 75.49	$ 59.72
Purchase Price	$ 300,500	$ 199,500
January 13, 2015
Equity, Class of Treasury Stock [Line Items]
Shares	2,870	0
Avg. Price per Share	$ 82.60	$ 0.00
Purchase Price	$ 237,072	$ 0