v3.24.0.1
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - OCI and tax effects (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Pre-Tax Amount      
Other comprehensive income (loss) $ (1.5) $ (49.2) $ (66.8)
Tax (Expense) Benefit      
Other comprehensive income (loss) 0.6   (0.2)
Net-of-Tax Amount      
Realized loss on foreign currency transactions reclassified into investment income, net of tax     (0.4)
Other comprehensive loss: (0.9) (49.2) (67.0)
Foreign Currency      
Pre-Tax Amount      
Unrealized foreign currency translation adjustment 0.5 (59.8) (78.9)
Realized gain (loss) on foreign currency transactions, net of tax     (0.9)
Tax (Expense) Benefit      
Unrealized foreign currency translation adjustment 0.6    
Realized gain (loss) on foreign currency transactions, net of tax     0.5
Net-of-Tax Amount      
Unrealized foreign currency translation adjustment 1.1 (59.8) (78.9)
Realized loss on foreign currency transactions reclassified into investment income, net of tax     (0.4)
Pension and other benefit adjustments      
Pre-Tax Amount      
Unrealized foreign currency translation adjustment (2.0) 10.6 13.0
Tax (Expense) Benefit      
Unrealized foreign currency translation adjustment     (0.7)
Net-of-Tax Amount      
Unrealized foreign currency translation adjustment $ (2.0) $ 10.6 $ 12.3