v3.26.1
Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive (Loss) Income) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Net realized losses from sales and other $ (4.9) $ (18.8)
Income before income taxes 237.1 160.1
Income tax (expense) benefit (50.3) (31.9)
Net income 186.8 128.2
Reclassification out of Accumulated Other Comprehensive Loss [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Net income (6.1) (15.8)
Net Unrealized Appreciation (Depreciation) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Net realized losses from sales and other (5.6) (18.8)
(Impairments) recoveries on investments (0.5) 0.1
Income before income taxes (6.1) (18.7)
Income tax (expense) benefit 1.4 4.3
Net income (4.9) (14.6)
Net Unrealized Appreciation (Depreciation) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member] | Accelerated Share Repurchase Agreement [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Income from continuing operations (4.7) (14.4)
Net Unrealized Appreciation (Depreciation) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member] | Life [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Income from discontinued life businesses 0.2 0.2
Defined Benefit Pension and Postretirement Plans [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Income before income taxes 1.7 1.7
Income tax (expense) benefit 0.3 0.3
Income from continuing operations (1.4) (1.4)
Net change in market risk | Reclassification out of Accumulated Other Comprehensive Loss [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Income tax (expense) benefit (0.1) (0.1)
Income from discontinued life businesses (0.2) (0.2)
Net change in market risk | Reclassification out of Accumulated Other Comprehensive Loss [Member] | Life [Member]    
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]    
Income from discontinued life businesses $ 0.3 $ 0.3