v3.26.1
Shareholders' equity (accumulated other comprehensive loss) (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Jun. 30, 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 0.0
Amounts reclassified from accumulated other comprehensive loss (0.4) (0.1)
Net current-period other comprehensive loss (0.4) (0.1)
Balance, end of period (6.8) (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 (1.0) 1.1
Amounts reclassified from accumulated other comprehensive loss 0.0 0.0
Net current-period other comprehensive loss (1.0) 1.1
Balance, end of period (13.1) (12.2)
Accumulated other comprehensive loss [Member]    
Accumulated other comprehensive loss [Line Items]    
Balance, beginning of period (18.5) (29.9)
Other comprehensive loss before reclassifications (1.0) 1.1
Amounts reclassified from accumulated other comprehensive loss (0.4) (0.1)
Net current-period other comprehensive loss (1.4) 1.0
Balance, end of period $ (19.9) $ (28.9)