Common Shares (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Jan. 31, 2014	Apr. 30, 2013
Common Shares Information
Common shares authorized	300,000,000	150,000,000
Common shares outstanding	104,544,135	106,486,935
Treasury shares	24,061,030	22,118,230
Common Shares (Additional Textual) [Abstract]
Shares repurchased during period	2,100,000	4,000,000
Purchase amount for shares repurchased	$ 213.6	$ 359.4
Shares remaining for repurchase	2,900,000
Common shares authorized	300,000,000	150,000,000