Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Millions	Jul. 31, 2018	Apr. 30, 2018
Allowance for doubtful accounts	$ 7	$ 7
Treasury stock, shares	3,372,000	3,531,000
Common stock, Class A, voting [Member]
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	170,000,000	170,000,000
Common stock, shares issued	170,000,000	170,000,000
Common stock, Class B, nonvoting [Member]
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	314,532,000	314,532,000