Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Millions, except Share data	Jul. 31, 2011	Apr. 30, 2011
Assets
Allowance for doubtful accounts	$ 17.6	$ 17.8
Common stock:
Treasury stock	11,540,000	11,337,000
Common stock, Class A, voting [Member]
Common stock:
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 [Member]
Common stock:
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	99,363,000	99,363,000