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Common Shares (Details) - shares
9 Months Ended
Jan. 31, 2020
Jan. 31, 2019
Apr. 30, 2019
Common Shares Information      
Common shares authorized 300,000,000.0   300,000,000.0
Common shares outstanding 114,000,000.0   113,700,000
Treasury shares 32,500,000   32,800,000
Common Shares (Additional Textual) [Abstract]      
Stock Repurchased During Period, Shares 0 0  
Shares remaining for repurchase 3,600,000