Common Shares (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Jul. 31, 2013	Apr. 30, 2013	Aug. 14, 2013 [SubsequentEventMember]
Common Shares Information
Common shares authorized	150,000,000	150,000,000	300,000,000
Common shares outstanding	105,130,165	106,486,935
Treasury shares	23,475,000	22,118,230
Common Shares (Textual) [Abstract]
Common shares authorized	150,000,000	150,000,000	300,000,000
Common Shares (Additional Textual) [Abstract]
Shares repurchased during period	1,500,000	4,000,000
Purchase amount for shares repurchased	$ 152.2	$ 359.4
Shares remaining for repurchase	3,400,000
Common shares authorized	150,000,000	150,000,000	300,000,000