v3.19.3.a.u2
ACCUMULATED OTHER COMPREHENSIVE INCOME - OCI and tax effects (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Pre-Tax Amount      
Realized loss on foreign currency transactions $ 0.5    
Other comprehensive income (loss), before tax (34.0) $ (124.7) $ 139.1
Tax (Expense) Benefit      
Realized loss on foreign currency transactions, tax   1.0  
Other comprehensive income (loss), tax 2.4 0.2 (11.0)
Net-of-Tax Amount      
Realized loss on foreign currency transactions reclassified into other expense, net of tax 0.5 1.0  
Realized net gain reclassified into investment income, net of tax     (0.4)
Other comprehensive income (loss): (31.6) (124.5) 128.1
Foreign Currency      
Pre-Tax Amount      
Unrealized net holding gain (loss) arising during the period (18.3) (127.5) 142.6
Tax (Expense) Benefit      
Unrealized net holding gain (loss) arising during the period, tax 1.8 (0.2) (10.9)
Net-of-Tax Amount      
Unrealized net holding gain (loss) arising during the period, net of tax (16.5) (127.7) 131.7
Reclassification adjustment for net gain (loss) realized in net earnings, net of tax 0.5 1.0  
Other comprehensive income (loss):   (126.7)  
Foreign Currency | Accounting Standards Update 2018-02 [Member]      
Net-of-Tax Amount      
Reclassification adjustment for net gain (loss) realized in net earnings, net of tax   4.0  
Pension and Other Benefit Adjustments, Net Gain or Loss      
Pre-Tax Amount      
Unrealized net holding gain (loss) arising during the period (16.1) 3.8 (2.6)
Tax (Expense) Benefit      
Unrealized net holding gain (loss) arising during the period, tax 0.6 0.4 (0.4)
Net-of-Tax Amount      
Unrealized net holding gain (loss) arising during the period, net of tax (15.5) 4.2 (3.0)
Unrealized Gains from Marketable Securities (Recorded in Investment income)      
Pre-Tax Amount      
Unrealized net holding gain (loss) arising during the period     1.2
Realized net (gain) loss reclassified into investment expense (income)     (0.6)
Tax (Expense) Benefit      
Unrealized net holding gain (loss) arising during the period, tax     (0.5)
Realized net (gain) loss reclassified into investment income, tax     0.2
Net-of-Tax Amount      
Unrealized net holding gain (loss) arising during the period, net of tax     0.7
Realized net gain reclassified into investment income, net of tax     (0.4)
Unrealized Gains from Marketable Securities (Recorded in Investment income) | Accounting Standards Update 2016-01 [Member]      
Net-of-Tax Amount      
Reclassification adjustment for net gain (loss) realized in net earnings, net of tax   (0.6)  
Unrealized Gain from Equity Method Investees' Cash Flow Hedge      
Pre-Tax Amount      
Unrealized net holding gain (loss) arising during the period (0.1) 0.2  
Reclassification adjustment for net gain (loss) realized in net earnings   (2.2) (1.5)
Tax (Expense) Benefit      
Reclassification adjustment for net gain (loss) realized in net earnings, tax     0.6
Net-of-Tax Amount      
Unrealized net holding gain (loss) arising during the period, net of tax $ (0.1) 0.2  
Reclassification adjustment for net gain (loss) realized in net earnings, net of tax   (2.2) $ (0.9)
Other comprehensive income (loss):   (2.0)  
Unrealized Gain from Equity Method Investees' Cash Flow Hedge | Accounting Standards Update 2018-02 [Member]      
Net-of-Tax Amount      
Reclassification adjustment for net gain (loss) realized in net earnings, net of tax   $ 0.4