Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Millions	Jan. 31, 2016	Apr. 30, 2015
Allowance for doubtful accounts	$ 9	$ 10
Treasury stock, shares	26,160,000	18,613,000
Common stock, Class A, voting [Member]
Common stock, shares authorized	85,000,000	85,000,000
Common stock, shares issued	85,000,000	85,000,000
Common stock, Class B, nonvoting [Member]
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	142,313,000	142,313,000