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, 2016		179,598				75,385
Beginning 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)
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	884,981			884,981
Comprehensive income (loss), net of tax	(55,495)				(55,495)
Dividends	(220,764)			(220,764)
Stock-based compensation	139,210		139,210
Vesting of stock-based compensation awards (shares)		766
Vesting of stock-based compensation awards	0	$ 156,493	(156,493)
Stock options exercised, net of shares surrendered (in shares)		1,302
Stock options exercised, net of shares surrendered	65,371	$ 65,371
Repurchase of common stock (shares)						(5,109)
Repurchase of common stock	(1,016,300)					$ (1,016,300)
Balance (shares) at May. 31, 2019		184,791				81,506
Ending Balance at May. 31, 2019	$ 3,002,721	$ 840,328	$ 227,928	$ 6,691,236	$ (39,152)	$ (4,717,619)