Common Shares (Details) - shares	6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 22, 2021	Jul. 31, 2021	Apr. 30, 2021
Common Shares Information
Common shares authorized	300,000,000.0				300,000,000.0
Common shares outstanding	108,400,000				108,300,000
Treasury shares	38,100,000				38,200,000
Common Shares (Additional Textual) [Abstract]
Shares repurchased	0	0
Shares authorized to be repurchased under stock repurchase program			5,000,000
Shares remaining for repurchase	7,800,000			2,800,000