Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Other Accumulated Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Balance at May. 31, 2011	$ 2,302,649	$ 135,401	$ 95,732	$ 3,255,256	$ 58,807	$ (1,242,547)
Balance (shares) at May. 31, 2011		173,346,000
Balance, Treasury Stock (shares) at May. 31, 2011						(35,762,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	297,637			297,637
Comprehensive income (loss), net of tax	(22,144)				(22,144)
Dividends	(70,820)			(70,820)
Stock-based compensation	20,312		20,312
Vesting of stock-based compensation awards (shares)		297,000
Vesting of stock-based compensation awards	0	9,513	(9,513)
Stock options exercised, net of shares surrendered (shares)		103,000
Stock options exercised, net of shares surrendered	3,341	3,341
Repurchase of common stock (shares)						(11,464,000)
Repurchase of common stock	(392,328)					(392,328)
Other	488		488
Balance at May. 31, 2012	2,139,135	148,255	107,019	3,482,073	36,663	(1,634,875)
Balance (shares) at May. 31, 2012		173,746,000
Balance, Treasury Stock (shares) at May. 31, 2012						(47,226,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	315,442			315,442
Comprehensive income (loss), net of tax	1,460				1,460
Dividends	(79,744)			(79,744)
Stock-based compensation	23,310		23,310
Vesting of stock-based compensation awards (shares)		610,000
Vesting of stock-based compensation awards	0	23,270	(23,270)
Stock options exercised, net of shares surrendered (shares)		430,000
Stock options exercised, net of shares surrendered	14,807	14,807
Repurchase of common stock (shares)						(5,279,000)
Repurchase of common stock	(215,681)					(215,681)
Other	2,763		2,763
Balance at May. 31, 2013	2,201,492	186,332	109,822	3,717,771	38,123	(1,850,556)
Balance (shares) at May. 31, 2013		174,786,000
Balance, Treasury Stock (shares) at May. 31, 2013	(52,504,503)					(52,505,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	374,442			374,442
Comprehensive income (loss), net of tax	(9,695)				(9,695)
Dividends	(93,320)			(93,320)
Stock-based compensation	44,746		44,746
Vesting of stock-based compensation awards (shares)		465,000
Vesting of stock-based compensation awards	0	23,519	(23,519)
Stock options exercised, net of shares surrendered (shares)		1,127,000
Stock options exercised, net of shares surrendered	41,902	41,902
Repurchase of common stock (shares)						(6,836,000)
Repurchase of common stock	(370,599)					(370,599)
Other	3,890		3,890
Balance at May. 31, 2014	$ 2,192,858	$ 251,753	$ 134,939	$ 3,998,893	$ 28,428	$ (2,221,155)
Balance (shares) at May. 31, 2014		176,378,000
Balance, Treasury Stock (shares) at May. 31, 2014	(59,340,628)					(59,341,000)