Common Shares (Details) - shares	6 Months Ended
	Oct. 31, 2018	Apr. 30, 2018
Stockholders' Equity Note [Abstract]
Stock Repurchased During Period, Shares	0
Common Shares Information
Common shares authorized	300,000,000.0	300,000,000
Common shares outstanding	113,800,000	113,600,000
Treasury shares	32,700,000	32,900,000
Common Shares (Additional Textual) [Abstract]
Shares remaining for repurchase	3,600,000