Consolidated Statements of Stockholders' Equity (USD $) In Millions, except Share data in Thousands, unless otherwise specified	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]
Beginning Balance at Apr. 30, 2011		$ 9	$ 15	$ 55	$ 2,710	$ (131)	$ (598)
Beginning Balance (shares) at Apr. 30, 2011		56,561	88,429
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock split		0	0		0		0
Stock split (shares)		0	0
Stock-based compensation expense				9
Loss on issuance of treasury stock issued under compensation plans				23	0
Excess tax benefits from stock-based awards				8
Net income	513				513
Cash dividends ($0.89, $4.98, and $1.09 per share in 2012, 2013, and 2014, respectively)					(192)
Net other comprehensive (loss) income	(99)					(99)
Acquisition of treasury stock							(220)
Stock issued under compensation plans							13
Acquisition of treasury stock (shares)		(310)	(2,851)
Stock issued under compensation plans (shares)		0
Stock issued under compensation plans (shares)			245
Total common shares outstanding (shares)	142,074	56,251	85,823
Ending Balance at Apr. 30, 2012	2,069	9	15	49	3,031	(230)	(805)
Ending Balance (shares) at Apr. 30, 2012	142,074	56,251	85,823
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock split		4	6		(18)		8
Stock split (shares)		28,149	42,951
Stock-based compensation expense				11
Loss on issuance of treasury stock issued under compensation plans				6	41
Excess tax benefits from stock-based awards				17
Net income	591				591
Cash dividends ($0.89, $4.98, and $1.09 per share in 2012, 2013, and 2014, respectively)					(1,063)
Net other comprehensive (loss) income	19					19
Acquisition of treasury stock							0
Stock issued under compensation plans							31
Acquisition of treasury stock (shares)		0	0
Stock issued under compensation plans (shares)		46
Stock issued under compensation plans (shares)			487
Total common shares outstanding (shares)	213,707	84,446	129,261
Ending Balance at Apr. 30, 2013	1,628	13	21	71	2,500	(211)	(766)
Ending Balance (shares) at Apr. 30, 2013	213,707	84,446	129,261
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock split		0	0		0		0
Stock split (shares)		0	0
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 ($0.89, $4.98, and $1.09 per share in 2012, 2013, and 2014, respectively)					(233)
Net other comprehensive (loss) income	23					23
Acquisition of treasury stock							(49)
Stock issued under compensation plans							26
Acquisition of treasury stock (shares)		(46)	(661)
Stock issued under compensation plans (shares)		62
Stock issued under compensation plans (shares)			393
Total common shares outstanding (shares)	213,455	84,462	128,993
Ending Balance at Apr. 30, 2014	$ 2,032	$ 13	$ 21	$ 81	$ 2,894	$ (188)	$ (789)
Ending Balance (shares) at Apr. 30, 2014	213,455	84,462	128,993