Common Stock Rollforward of Outstanding Shares (Details) - shares shares in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Class of Stock [Line Items]
Beginning balance	480,106	494,353	521,749
Acquisition of treasury stock	(31)	(14,845)	(28,536)
Stock issued under compensation plans	926	598	1,140
Ending balance	481,001	480,106	494,353
Common stock, Class A, voting [Member]
Class of Stock [Line Items]
Beginning balance	169,051	169,060	168,926
Acquisition of treasury stock	(25)	(77)	(114)
Stock issued under compensation plans	36	68	248
Ending balance	169,062	169,051	169,060
Common Stock, Class B, nonvoting [Member]
Class of Stock [Line Items]
Beginning balance	311,055	325,293	352,823
Acquisition of treasury stock	(6)	(14,768)	(28,422)
Stock issued under compensation plans	890	530	892
Ending balance	311,939	311,055	325,293