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, 2014	$ 2,032	$ 13	$ 21	$ 81	$ 2,894	$ (188)	$ (789)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	684				684
Net other comprehensive income (loss)	(112)					(112)
Cash dividends	(256)				(256)
Acquisition of treasury stock	(462)						(462)
Stock-based compensation expense	15			15
Stock issued under compensation plans	23						23
Loss on issuance of treasury stock issued under compensation plans	(37)			(15)	(22)
Excess tax benefits from stock-based awards	18			18
Ending 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 11)	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)