Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member] Common stock, Class A, voting [Member]	Common Stock [Member] Common Stock, Class B, nonvoting [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock, Common [Member]
Beginning Balance at Apr. 30, 2016	$ 1,562	$ 13	$ 21	$ 114	$ 4,065	$ (350)	$ (2,301)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock split (Note 8)	0	12	22	(34)
Net income	669				669
Net other comprehensive income (loss)	(40)					(40)
Cash dividends	(274)				(274)
Acquisition of treasury stock	(561)						(561)
Stock-based compensation expense	14			14
Stock issued under compensation plans	19						19
Loss on issuance of treasury stock issued under compensation plans	(29)			(29)
Ending Balance at Apr. 30, 2017	1,370	25	43	65	4,470	(390)	(2,843)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retirement of treasury stock (Note 8)	0		(10)	(8)	(2,684)		2,702
Stock split (Note 8)	0		14	(14)
Net income	717				717
Net other comprehensive income (loss)	12					12
Cash dividends	(773)				(773)
Acquisition of treasury stock	(1)						(1)
Stock-based compensation expense	19			19
Stock issued under compensation plans	30						30
Loss on issuance of treasury stock issued under compensation plans	(58)			(58)
Ending Balance at Apr. 30, 2018	1,316	25	47	4	1,730	(378)	(112)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	835				835
Net other comprehensive income (loss)	15					15
Cash dividends	(310)				(310)
Acquisition of treasury stock	(207)						(207)
Stock-based compensation expense	14			14
Stock issued under compensation plans	19						19
Loss on issuance of treasury stock issued under compensation plans	(30)			(18)	(12)
Ending Balance at Apr. 30, 2019	$ 1,647	$ 25	$ 47	$ 0	$ 2,238	$ (363)	$ (300)