Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Apr. 30, 2012	Apr. 30, 2011
Allowance for doubtful accounts	$ 9	$ 18
Unamortized discount	$ 1	$ 2
Treasury stock, shares	14,253,000	11,337,000
Common stock, Class A, voting [Member]
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	57,000,000	57,000,000
Common stock, shares issued	56,964,000	56,964,000
Common stock, Class B, nonvoting
Common stock, par value	$ 0.15	$ 0.15
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	99,363,000	99,363,000