Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-In Capital	Retained Earnings	Other Accumulated Comprehensive Income (Loss)	Treasury Stock
Balance (shares) at May. 31, 2015		178,117				66,414
Beginning Balance at May. 31, 2015	$ 1,932,455	$ 329,248	$ 157,183	$ 4,227,620	$ (8,471)	$ (2,773,125)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	693,520			693,520
Comprehensive income (loss), net of tax	(16,403)				(16,403)
Dividends	(115,273)			(115,273)
Stock-based compensation	79,293		79,293
Vesting of stock-based compensation awards (shares)		605
Vesting of stock-based compensation awards	0	$ 52,208	(52,208)
Stock options exercised, net of shares surrendered (in shares)		876
Stock options exercised, net of shares surrendered	28,226	$ 28,226
Repurchase of common stock (shares)						(8,971)
Repurchase of common stock	(780,151)					$ (780,151)
Other	20,992		20,992
Balance (shares) at May. 31, 2016		179,598				75,385
Ending Balance at May. 31, 2016	1,842,659	$ 409,682	205,260	4,805,867	(24,874)	$ (3,553,276)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	480,708			480,708
Comprehensive income (loss), net of tax	21,845				21,845
Dividends	(142,433)			(142,433)
Stock-based compensation	88,868		88,868
Vesting of stock-based compensation awards (shares)		429
Vesting of stock-based compensation awards	0	$ 43,516	(43,516)
Stock options exercised, net of shares surrendered (in shares)		966
Stock options exercised, net of shares surrendered	31,870	$ 31,870
Repurchase of common stock (shares)						(207)
Repurchase of common stock	(20,724)					$ (20,724)
Adoption of new accounting guidance	0		(26,688)	26,688
Balance (shares) at May. 31, 2017		180,993				75,592
Ending Balance at May. 31, 2017	2,302,793	$ 485,068	223,924	5,170,830	(3,029)	$ (3,574,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	842,586			842,586
Comprehensive income (loss), net of tax	19,372				19,372
Dividends	(175,589)			(175,589)
Stock-based compensation	112,835		112,835
Vesting of stock-based compensation awards (shares)		701
Vesting of stock-based compensation awards	0	$ 91,548	(91,548)
Stock options exercised, net of shares surrendered (in shares)		1,029
Stock options exercised, net of shares surrendered	41,848	$ 41,848
Repurchase of common stock (shares)						(805)
Repurchase of common stock	(127,319)					$ (127,319)
Balance (shares) at May. 31, 2018		182,723				76,397
Ending Balance at May. 31, 2018	$ 3,016,526	$ 618,464	$ 245,211	$ 5,837,827	$ 16,343	$ (3,701,319)