v3.25.4
Investments - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
USD ($)
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Debt and Equity Securities, FV-NI [Line Items]      
Other receivables $ 184.7 $ 185.7  
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date $ 1,684.7    
Debt securities, available-for-sale, unrealized loss amount, average, percentage 0.033    
Financing receivable, accrued interest, before allowance for credit loss $ 75.3 70.9  
Investments in Equity Securities at Fair Value 306.4 218.5  
Unrealized gain (loss) on Investments in Equity Securities at Fair Value (4.1) (5.1)  
Equity Method Limited Liability Investments 176.0 186.3  
Outstanding commitments to fund equity method limited liability investments $ 97.5    
Equity method investments, reported without a reporting lag 0.031    
Equity method investments, reported with a one-moth reporting lag 0.017    
Carrying values of the COLI investment $ 579.2 539.2  
Loans to Policyholders 279.9 280.7  
Other Investments and Securities, at Cost 21.7 22.5  
Impairment Losses 10.8 5.8 $ 1.1
Debt and equity securities, gain (loss), excluding other-than-temporary impairment loss 3.2 3.2  
Dividends on Equity Securities Excluding Alternative Investments      
Debt and Equity Securities, FV-NI [Line Items]      
Impairment Losses 0.0 0.4 $ 0.5
Investments in Fixed Maturities      
Debt and Equity Securities, FV-NI [Line Items]      
Other receivables 1.6 1.8  
Other liabilities 42.7 11.6  
Debt securities, available-for-sale, unrealized loss position, accumulated loss 733.1 889.5  
Government National Mortgage Association Certificates and Obligations (GNMA)      
Debt and Equity Securities, FV-NI [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 345.2    
Federal National Mortgage Association Certificates and Obligations (FNMA)      
Debt and Equity Securities, FV-NI [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 84.9    
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)      
Debt and Equity Securities, FV-NI [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 58.4    
Other Non-Governmental Issuers      
Debt and Equity Securities, FV-NI [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 1,196.2    
Foreign Governments      
Debt and Equity Securities, FV-NI [Line Items]      
Debt securities, available-for-sale, unrealized loss position, accumulated loss 0.1 0.2  
Bonds and Notes      
Debt and Equity Securities, FV-NI [Line Items]      
Debt securities, available-for-sale, unrealized loss position, accumulated loss 433.5 518.8  
Equity Method Limited Liability Investments at Cost Plus Cumulative Undistributed Earnings      
Debt and Equity Securities, FV-NI [Line Items]      
Other liabilities 0.0 0.0  
Dividends on Equity Securities Excluding Alternative Investments      
Debt and Equity Securities, FV-NI [Line Items]      
Other receivables 0.2 0.3  
Other liabilities 0.0 0.0  
Investment-grade | Investments in Fixed Maturities      
Debt and Equity Securities, FV-NI [Line Items]      
Debt securities, available-for-sale, unrealized loss position, accumulated loss 719.6 875.3  
Non-investment-grade | Investments in Fixed Maturities      
Debt and Equity Securities, FV-NI [Line Items]      
Debt securities, available-for-sale, unrealized loss position, accumulated loss $ 13.6 $ 14.2  
Percentage of unrealized loss position to amortized cost basis of available for sale security average   4.90%