Common Stock Rollforward of Issued Shares (Details) - shares	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Class of Stock [Line Items]
Beginning balance	454,626,000	227,313,000
Retirement of treasury stock	(67,000,000)
Stock split	96,906,000	227,313,000
Ending balance	484,532,000	454,626,000
Common stock, Class A, voting [Member]
Class of Stock [Line Items]
Beginning balance	170,000,000	85,000,000
Retirement of treasury stock	0
Stock split	0	85,000,000
Ending balance	170,000,000	170,000,000
Common Stock, Class B, nonvoting [Member]
Class of Stock [Line Items]
Beginning balance	284,626,000	142,313,000
Retirement of treasury stock	(67,000,000)
Stock split	96,906,000	142,313,000
Ending balance	314,532,000	284,626,000