v3.26.1
Investments - Schedule of Fixed Maturities (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost $ 7,495.1 $ 7,475.7
Gross unrealized gains 13.2 20.8
Gross unrealized loss (763.8) (733.1)
Fixed maturities, allowance for credit losses (23.4) (20.1)
Fair Value 6,721.1 6,743.3
U.S. Government and Government Agencies and Authorities    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 725.7 702.0
Gross unrealized gains 1.4 3.2
Gross unrealized loss (85.3) (82.8)
Fixed maturities, allowance for credit losses 0.0 0.0
Fair Value 641.8 622.4
States and Political Subdivisions    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 1,412.9 1,437.3
Gross unrealized gains 1.1 1.8
Gross unrealized loss (180.7) (185.7)
Fixed maturities, allowance for credit losses 0.0 (0.2)
Fair Value 1,233.3 1,253.2
Foreign Governments    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 8.4 10.7
Gross unrealized gains 0.2 0.4
Gross unrealized loss (0.1) (0.1)
Fixed maturities, allowance for credit losses 0.0 0.0
Fair Value 8.5 11.0
Corporate Bonds and Notes    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 4,185.3 4,089.8
Gross unrealized gains 8.4 11.4
Gross unrealized loss (464.6) (433.5)
Fixed maturities, allowance for credit losses (18.8) (17.4)
Fair Value 3,710.3 3,650.3
Redeemable Preferred Stocks    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 9.5 9.8
Gross unrealized gains 0.3 0.4
Gross unrealized loss 0.0 0.0
Fixed maturities, allowance for credit losses 0.0 0.0
Fair Value 9.8 10.2
Collateralized Loan Obligations    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 781.5 850.8
Gross unrealized gains 1.1 2.5
Gross unrealized loss (9.2) (7.8)
Fixed maturities, allowance for credit losses (4.6) (2.5)
Fair Value 768.8 843.0
Other Mortgage- and Asset-backed    
Debt Securities, Available-for-sale [Line Items]    
Fixed maturities, at amortized cost 371.8 375.3
Gross unrealized gains 0.7 1.1
Gross unrealized loss (23.9) (23.2)
Fixed maturities, allowance for credit losses 0.0 0.0
Fair Value $ 348.6 $ 353.2