v3.21.2
BASIS OF PRESENTATION - AOCL and Accumulated Depreciation and Amortization (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2021
Dec. 31, 2020
Accumulated other comprehensive loss      
Balance at the beginning of the period   $ (2,885.1)  
Realized loss on foreign currency transactions reclassified into investment expense (income) $ (0.9) (0.9)  
Balance at the end of the period (1,404.7) (1,404.7)  
Accumulated depreciation and amortization      
Accumulated depreciation 2,417.7 2,417.7 $ 2,243.1
Accumulated amortization 43.3 43.3 $ 42.0
Foreign Currency      
Accumulated other comprehensive loss      
Balance at the beginning of the period   60.1  
Other comprehensive income (loss)   (33.4)  
Realized loss on foreign currency transactions reclassified into investment expense (income)   (0.9)  
Balance at the end of the period 25.8 25.8  
Pension Benefits      
Accumulated other comprehensive loss      
Balance at the beginning of the period   (21.4)  
Other comprehensive income (loss)   3.8  
Balance at the end of the period (17.6) (17.6)  
Accumulated Other Comprehensive Income (Loss)      
Accumulated other comprehensive loss      
Balance at the beginning of the period   38.7  
Other comprehensive income (loss)   (29.6)  
Realized loss on foreign currency transactions reclassified into investment expense (income)   (0.9)  
Balance at the end of the period $ 8.2 $ 8.2