v3.26.1
Investments Net Investment Income (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Gain (Loss) on Securities [Line Items]        
Gross investment income $ 187.4 $ 176.9 $ 370.5 $ 353.1
Investment expenses [1] 5.4 5.4 10.4 10.8
Net Investment Income, Total 182.0 171.5 360.1 342.2
Net realized gains (losses) 136.2 (4.7) 295.7 38.5
Equity Securities, FV-NI, Unrealized Gain (Loss) 134.2 (4.9) 250.7 12.7
Gain (Loss) on Investments 172.4 (7.3) 374.3 47.7
Income Taxes Credits On Realized Investment Gains Losses 36.2 (2.6) 78.6 9.1
Changes in unrealized investment gains (losses) on investments (43.0) 90.6 (186.3) 232.3
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax (8.9) 19.0 (39.1) 48.9
Net unrealized gains (losses) on securities, net of tax (34.0) 71.6 (147.2) 183.3
Debt Securities, Available-for-sale, Realized Gain 3.1 1.5 6.0 2.1
Debt Securities, Available-for-sale, Realized Loss 7.5 4.1 7.8 5.8
Debt Securities, Available-for-sale, Realized Gain (Loss) (4.3) (2.6) (1.8) (3.6)
OtherThanTemporaryImpairmentLossesCreditLossesOtherInvestmentsDebtSecuritiesSaleOfSubsidiaryRecognizedInEarnings (3.8) 0.0 (13.8) 0.0
Realized Investment Gains Losses From Sales 42.0 (2.4) 137.3 34.9
Equity Securities [Member]        
Gain (Loss) on Securities [Line Items]        
Equity securities, gross realized gains 46.0 11.4 138.9 51.4
Equity securities, gross realized losses 0.0 (11.3) 0.0 (12.4)
Equity securities, net realized gains (losses) 46.0 0.1 138.8 38.9
Fixed Income Securities [Member]        
Gain (Loss) on Securities [Line Items]        
Changes in unrealized investment gains (losses) on investments (42.9) 90.6 (186.0) 230.6
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax (8.9) 19.0 (39.0) 48.6
Net changes in unrealized investment gains (losses) (33.9) 71.6 (146.9) 182.0
Other long-term investments [Member]        
Gain (Loss) on Securities [Line Items]        
Changes in unrealized investment gains (losses) on investments (0.1) 0.0 (0.2) 1.6
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax 0.0 0.0 0.0 0.3
Net changes in unrealized investment gains (losses) 0.0 0.0 (0.2) 1.3
Other than Securities Investment        
Gain (Loss) on Securities [Line Items]        
Investment gains (losses) - other investments 0.3 0.0 0.3 (0.3)
Fixed Income Securities [Member]        
Gain (Loss) on Securities [Line Items]        
Gross investment income 149.1 141.2 298.4 279.8
Equity Securities [Member]        
Gain (Loss) on Securities [Line Items]        
Gross investment income 18.9 20.9 38.0 41.7
Short-term Investments [Member]        
Gain (Loss) on Securities [Line Items]        
Gross investment income 12.7 11.8 23.7 23.8
Investments [Member]        
Gain (Loss) on Securities [Line Items]        
Gross investment income [1] $ 6.5 $ 2.8 $ 10.2 $ 7.6
[1]
(a) Includes interest on funds held.