Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	[1]	Feb. 29, 2016	[1]	Nov. 30, 2015	[1]	Aug. 31, 2015	[1]	May 31, 2017	May 31, 2016	May 31, 2015
Quarterly Financial Data [Abstract]
Revenue	$ 1,530,287	$ 1,255,367	$ 1,271,077	$ 1,266,650	$ 1,243,548		$ 1,190,539		$ 1,191,121		$ 1,170,564		$ 5,323,381	$ 4,795,772	$ 4,369,677
Gross margin	678,726	559,924	565,218	576,427	546,371		517,853		520,221		516,895		2,380,295	2,101,340	1,892,923
Net income, continuing operations	$ 82,174	$ 116,954	$ 121,950	$ 136,208	$ 115,711		$ 115,122		$ 113,447		$ 104,325		$ 457,286	$ 448,605	$ 402,553
Basic earnings per share, continuing operations (dollars per share)	$ 0.76	$ 1.09	$ 1.15	$ 1.27	$ 1.07		$ 1.05		$ 1.03		$ 0.93		$ 4.27	$ 4.08	$ 3.44
Diluted earnings per share from continuing operations (in dollars per share)	$ 0.75	$ 1.06	$ 1.12	$ 1.24	$ 1.06		$ 1.03		$ 1.01		$ 0.92		$ 4.17	$ 4.02	$ 3.39
Weighted average number of shares outstanding (shares)	105,325	105,093	104,957	104,483	106,136		107,843		108,301		110,597		104,964	108,221	115,900

[1] The figures for fiscal 2016 reflect the change in classification of Discontinued Services as discontinued operations within the Consolidated Statements of Income. See Note 16 entitled Discontinued Operations for additional information.