Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common stock, Class A, voting [Member]	Common Stock, Class B, nonvoting [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income, Net of Tax [Member]	Treasury Stock, at Cost [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total common shares outstanding (shares)		84,446	129,261
Beginning Balance at Apr. 30, 2013				$ 71	$ 2,500	$ (211)	$ (766)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense				13
Loss on issuance of treasury stock issued under compensation plans				(13)	(32)
Excess tax benefits from stock-based awards				10
Net income	$ 659				659
Cash dividends ($1.09, $1.21, and $1.31 per share in 2014, 2015, and 2016, respectively)					(233)
Net other comprehensive (loss) income	23					23
Acquisition of treasury stock							(49)
Stock issued under compensation plans							26
Ending Balance at Apr. 30, 2014	$ 2,032	$ 13	$ 21	81	2,894	(188)	(789)
Beginning Balance (shares) at Apr. 30, 2013		84,446	129,261
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition of treasury stock (shares)		(46)	(661)
Stock issued under compensation plans (shares)		62
Stock issued under compensation plans (shares)			393
Ending Balance (shares) at Apr. 30, 2014	213,455	84,462	128,993
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total common shares outstanding (shares)	213,455	84,446	129,261
Total common shares outstanding (shares)	213,455	84,462	128,993
Stock-based compensation expense				15
Loss on issuance of treasury stock issued under compensation plans				(15)	(22)
Excess tax benefits from stock-based awards				18
Net income	$ 684				684
Cash dividends ($1.09, $1.21, and $1.31 per share in 2014, 2015, and 2016, respectively)					(256)
Net other comprehensive (loss) income	(112)					(112)
Acquisition of treasury stock							(462)
Stock issued under compensation plans							23
Ending Balance at Apr. 30, 2015	$ 1,905	$ 13	$ 21	99	3,300	(300)	(1,228)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition of treasury stock (shares)		(85)	(5,034)
Stock issued under compensation plans (shares)		86
Stock issued under compensation plans (shares)			278
Ending Balance (shares) at Apr. 30, 2015	208,700	84,463	124,237
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total common shares outstanding (shares)	213,455	84,462	128,993
Total common shares outstanding (shares)	208,700	84,463	124,237
Stock-based compensation expense				15
Loss on issuance of treasury stock issued under compensation plans				(15)	(36)
Excess tax benefits from stock-based awards				15
Net income	$ 1,067				1,067
Cash dividends ($1.09, $1.21, and $1.31 per share in 2014, 2015, and 2016, respectively)					(266)
Net other comprehensive (loss) income	(50)					(50)
Acquisition of treasury stock							(1,107)
Stock issued under compensation plans							34
Ending Balance at Apr. 30, 2016	$ 1,562	$ 13	$ 21	$ 114	$ 4,065	$ (350)	$ (2,301)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition of treasury stock (shares)		(57)	(11,357)
Stock issued under compensation plans (shares)		124
Stock issued under compensation plans (shares)			332
Ending Balance (shares) at Apr. 30, 2016	197,742	84,530	113,212
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total common shares outstanding (shares)	208,700	84,463	124,237
Total common shares outstanding (shares)	197,742	84,530	113,212