Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Millions, except Share data, unless otherwise specified	Jan. 31, 2014	Apr. 30, 2013
Allowance for doubtful accounts	$ 9	$ 9
Treasury stock, shares	14,044,000	13,606,000
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