v3.26.1
Earnings per share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net earnings $ 39.9 $ 153.5 $ 46.6 $ 204.1
Weighted average number of shares outstanding, basic (in shares) 68.5 71.2 68.5 71.8
Basic net (loss)/earnings per common share (in dollars per share) $ 0.58 $ 2.16 $ 0.68 $ 2.84
Weighted average number of shares outstanding, diluted (in shares) 69.2 72.1 69.2 72.9
Diluted net (loss)/earnings per common share- continuing operations (in dollars per share) $ 0.58 $ 2.13 $ 0.67 $ 2.80
Performance Shares        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of dilutive performance shares (shares) 0.3 0.5 0.4 0.7
Restricted Stock Equivalents        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of dilutive performance shares (shares) 0.4 0.4 0.3 0.4