v3.25.4
Other Comprehensive Income (Loss) And Accumulated Other Comprehensive Loss - Other Comprehensive (Loss) Income (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent $ 2,681.4 $ 2,788.4   $ 241.1
Net Unrealized Losses on Fixed Maturities        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent (559.5) (687.8) $ (530.9) (719.4)
OCI, before Reclassifications, Net of Tax, Attributable to Parent 127.0 (165.8) 185.0  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent 1.3 8.9 3.5  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 128.3 (156.9) 188.5  
Net Unrealized Losses on Investments with an Allowance for Credit Losses        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent (3.0) (3.2) (2.5) (2.2)
OCI, before Reclassifications, Net of Tax, Attributable to Parent 0.2 (0.3) (0.3)  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent 0.0 (0.4) 0.0  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 0.2 (0.7) (0.3)  
Net Unrecognized Postretirement Benefit Income (Costs)        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent 6.1 8.4 9.5 37.2
OCI, before Reclassifications, Net of Tax, Attributable to Parent (0.7) 1.4 (6.0)  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent (1.6) (2.5) 52.7  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (2.3) (1.1) 46.7  
Net Gain (Loss) on Cash Flow Hedges        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent (0.6) (2.2) 2.5 2.8
OCI, before Reclassifications, Net of Tax, Attributable to Parent 1.8 (5.4) 0.0  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent (0.2) 0.7 (0.3)  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 1.6 (4.7) (0.3)  
Change in Discount Rate on Future Life Policyholder Benefits        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent 350.8 380.3 160.6  
OCI, before Reclassifications, Net of Tax, Attributable to Parent (29.5) 219.7 (80.5)  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent 0.0 0.0 0.0  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (29.5) 219.7 (80.5)  
Accumulated Other Comprehensive Loss        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Stockholders' Equity Attributable to Parent (206.2) (304.5) (360.8) $ (514.9)
OCI, before Reclassifications, Net of Tax, Attributable to Parent 98.8 49.6 98.2  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent (0.5) 6.7 55.9  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent $ 98.3 $ 56.3 $ 154.1