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Common Shares (Details) - USD ($)
$ in Millions
9 Months Ended
Jan. 31, 2022
Jan. 31, 2021
Apr. 30, 2021
Common Shares Information      
Common shares authorized 300,000,000.0   300,000,000.0
Common shares outstanding 108,500,000   108,300,000
Treasury shares 38,000,000.0   38,200,000
Equity, Class of Treasury Stock [Line Items]      
Payments to repurchase shares $ 7.7 $ 504.1  
Board Authorized Repurchased Plan      
Equity, Class of Treasury Stock [Line Items]      
Shares repurchased 0 4,500,000  
Payments to repurchase shares   $ 521.9  
Shares remaining for repurchase 7,800,000