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, 2015	$ 1,905	$ 13	$ 21	$ 99	$ 3,300	$ (300)	$ (1,228)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,067				1,067
Net other comprehensive income (loss)	(50)					(50)
Cash dividends	(266)				(266)
Acquisition of treasury stock	(1,107)						(1,107)
Stock-based compensation expense	15			15
Stock issued under compensation plans	34						34
Loss on issuance of treasury stock issued under compensation plans	(51)			(15)	(36)
Excess tax benefits from stock-based awards	15			15
Ending 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 10)	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 10)	0		(10)	(8)	(2,684)		2,702
Stock split (Note 10)	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)