Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Allowance for doubtful accounts	$ 9	$ 9
Unamortized discount	$ 3	$ 1
Treasury stock, shares	13,606,000	14,253,000
Common stock, Class A, voting [Member]
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	85,000,000	57,000,000
Common stock, shares issued	85,000,000	56,964,000
Common Stock, Class B, nonvoting [Member]
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	400,000,000	100,000,000
Common stock, shares issued	142,313,000	99,363,000