Common Stock (Details) - shares shares in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Class of Stock [Line Items]
Beginning balance	395,484	417,400	426,910
Acquisition of treasury stock	(11,876)	(22,828)	(10,240)
Stock issued under compensation plans	478	912	730
Ending balance	384,086	395,484	417,400
Common stock, Class A, voting [Member]
Class of Stock [Line Items]
Beginning balance	169,060	168,926	168,924
Acquisition of treasury stock	(77)	(114)	(171)
Stock issued under compensation plans	68	248	173
Ending balance	169,051	169,060	168,926
Common Stock, Class B, nonvoting [Member]
Class of Stock [Line Items]
Beginning balance	226,424	248,474	257,986
Acquisition of treasury stock	(11,799)	(22,714)	(10,069)
Stock issued under compensation plans	410	664	557
Ending balance	215,035	226,424	248,474