v3.25.2
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, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net earnings/(loss) $ 153.5 $ (43.8) $ 204.1 $ (9.5)
Weighted average number of shares outstanding, basic (in shares) 71.2 71.8 71.8 71.7
Basic net (loss)/earnings per common share (in dollars per share) $ 2.16 $ (0.61) $ 2.84 $ (0.13)
Weighted average number of shares outstanding, diluted (in shares) 72.1 71.8 72.9 71.7
Diluted net (loss)/earnings per common share- continuing operations (in dollars per share) $ 2.13 $ (0.61) $ 2.80 $ (0.13)
Performance Shares        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of dilutive performance shares (shares) 0.5 0.0 0.7 0.0
Restricted Stock Equivalents        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of dilutive performance shares (shares) 0.4 0.0 0.4 0.0