v3.26.1
Shareholders' equity (accumulated other comprehensive loss) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Postretirement benefit plans [Member]    
Accumulated other comprehensive loss [Line Items]    
Balance, beginning of period $ (6.4) $ (16.6)
Other comprehensive loss before reclassifications 0.0  
Amounts reclassified from accumulated other comprehensive loss (0.2) (0.1)
Net current-period other comprehensive loss (0.2) (0.1)
Balance, end of period (6.6) (16.7)
Currency translation adjustment [Member]    
Accumulated other comprehensive loss [Line Items]    
Balance, beginning of period (12.1) (13.3)
Other comprehensive loss before reclassifications (0.5)  
Net current-period other comprehensive loss (0.5) 0.0
Balance, end of period (12.6) (13.3)
Accumulated other comprehensive loss [Member]    
Accumulated other comprehensive loss [Line Items]    
Balance, beginning of period (18.5) (29.9)
Other comprehensive loss before reclassifications (0.5)  
Amounts reclassified from accumulated other comprehensive loss (0.2) (0.1)
Net current-period other comprehensive loss (0.7) (0.1)
Balance, end of period $ (19.2) $ (30.0)