v3.26.1
FAIR VALUE MEASUREMENTS - SIGNIFICANT UNOBSERVABLE (LEVEL 3) INPUTS (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance $ 302.4 $ 353.2 $ 249.7 $ 324.7
Gains (losses) included in net income $ (2.6) $ (1.1) $ (0.8) $ 0.5
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Income Extensible List Not Disclosed Flag Gains (losses) included in net income Gains (losses) included in net income Gains (losses) included in net income Gains (losses) included in net income
Gains (losses) included in accumulated other comprehensive loss $ 2.1 $ (2.3) $ (2.0) $ (0.3)
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Other Comprehensive Income Extensible List Not Disclosed Flag Gains (losses) included in accumulated other comprehensive loss Gains (losses) included in accumulated other comprehensive loss Gains (losses) included in accumulated other comprehensive loss Gains (losses) included in accumulated other comprehensive loss
Purchases $ 22.7 $ 82.8 $ 41.6 $ 254.4
Sales (1.4) (14.2) (2.6) (20.0)
Transfers into Level 3 23.4 149.6 48.8  
Transfers Into Level 3       115.1
Transfers out of Level 3 (20.2) (16.4)   (122.8)
Transfers out of Level 3     (8.3)  
Ending balance 326.4 551.6 326.4 551.6
Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period $ (2.6) $ (1.1) $ (0.8) $ 0.5
Fair Value Asset Recurring Basis Still Held Unrealized Gain Loss Statement Of Income Extensible List Not Disclosed Flag Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period
Change in unrealized gains or losses for the period included in other comprehensive loss for assets held at the end of the reporting period $ 1.6 $ (3.5) $ (3.3) $ (2.1)
Other invested assets   92.8   92.8
Fixed Maturities, Available for Sale        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 224.0 277.3 171.8 155.9
Gains (losses) included in net income (2.2) (2.2) (0.7) (0.5)
Gains (losses) included in accumulated other comprehensive loss 2.1 (2.3) (2.0) (0.3)
Purchases 22.6 82.8 41.2 234.4
Sales (1.3) (14.2) (2.4) (20.0)
Transfers into Level 3 23.4 129.6 48.8  
Transfers Into Level 3       115.1
Transfers out of Level 3 (20.2) (16.4)   (30.0)
Transfers out of Level 3     (8.3)  
Ending balance 248.4 454.6 248.4 454.6
Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period (2.2) (2.2) (0.7) (0.5)
Change in unrealized gains or losses for the period included in other comprehensive loss for assets held at the end of the reporting period 1.6 (3.5) (3.3) (2.1)
Equity Securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 73.9 73.3 73.7 73.4
Gains (losses) included in net income (0.4) 1.1 (0.2) 1.0
Gains (losses) included in accumulated other comprehensive loss 0.0 0.0 0.0 0.0
Purchases 0.0 0.0 0.0 20.0
Sales 0.0 0.0 0.0 0.0
Transfers into Level 3 0.0 20.0 0.0  
Transfers out of Level 3 0.0 0.0    
Transfers out of Level 3     0.0  
Ending balance 73.5 94.4 73.5 94.4
Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period (0.4) 1.1 (0.2) 1.0
Change in unrealized gains or losses for the period included in other comprehensive loss for assets held at the end of the reporting period 0.0 0.0 0.0 0.0
Trading Securities        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Transfers Into Level 3       0.0
Transfers out of Level 3       0.0
Other Invested Assets        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 4.5 2.6 4.2 95.4
Gains (losses) included in net income 0.0 0.0 0.1 0.0
Gains (losses) included in accumulated other comprehensive loss 0.0 0.0 0.0 0.0
Purchases 0.1 0.0 0.4 0.0
Sales (0.1) 0.0 (0.2) 0.0
Transfers into Level 3 0.0 0.0 0.0  
Transfers Into Level 3       0.0
Transfers out of Level 3 0.0 0.0   (92.8)
Transfers out of Level 3     0.0  
Ending balance 4.5 2.6 4.5 2.6
Change in unrealized gains or losses for the period included in net income for assets held at the end of the reporting period 0.0 0.0 0.1 0.0
Change in unrealized gains or losses for the period included in other comprehensive loss for assets held at the end of the reporting period $ 0.0 $ 0.0 $ 0.0 $ 0.0