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Investments - Narrative (Details) - USD ($)
 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date $ 1,658,900,000    
Financing Receivable, Accrued Interest, before Allowance for Credit Loss 73,500,000   $ 70,900,000
Equity securities, FV-NI, unrealized gain (loss) $ (2,300,000) $ (2,300,000)  
Percentage of Equity Method Limited Liability Investments reported with a lag 3.00%    
Percentage of Equity Method Limited Liability Investments reported with a One Month Lag 2.00%    
Loans to Policyholders $ 279,300,000   280,700,000
Equity Securities at Modified Cost 22,200,000   22,500,000
Equity securities without readily determinable fair value, impairment loss, cumulative amount 3,200,000   3,200,000
Equity Securities      
Debt Securities, Available-for-sale [Line Items]      
Other Asset Impairment Charges 0 $ 400,000  
Alternative Energy Partnership Investments      
Debt Securities, Available-for-sale [Line Items]      
Alternative Energy Partnership Investments 17,400,000   17,600,000
Investments in Fixed Maturities      
Debt Securities, Available-for-sale [Line Items]      
Other Receivables 4,200,000   1,800,000
Other liabilities 7,800,000   11,600,000
Debt securities, available-for-sale, unrealized loss position, accumulated loss 728,000,000.0   889,500,000
Government National Mortgage Association Certificates and Obligations (GNMA)      
Debt Securities, Available-for-sale [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 326,100,000    
Federal National Mortgage Association Certificates and Obligations (FNMA)      
Debt Securities, Available-for-sale [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 85,400,000    
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)      
Debt Securities, Available-for-sale [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 58,700,000    
Other Non-Governmental Issuers      
Debt Securities, Available-for-sale [Line Items]      
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date 1,188,700,000    
Equity Securities      
Debt Securities, Available-for-sale [Line Items]      
Other Receivables     300,000
Other liabilities 0   0
Equity Method Investments      
Debt Securities, Available-for-sale [Line Items]      
Other liabilities 0   0
Consolidated Entity, Excluding VIE      
Debt Securities, Available-for-sale [Line Items]      
Other Receivables 185,000,000.0   185,700,000
Equity Securities, FV-NI, Current 302,000,000.0   218,500,000
Alternative Energy Partnership Investments 174,900,000   186,300,000
Loans to Policyholders 279,300,000   280,700,000
Variable Interest Entity, Not Primary Beneficiary | Equity Method Limited Liability Investments      
Debt Securities, Available-for-sale [Line Items]      
Outstanding commitments to fund equity method limited liability investments 102,600,000    
Investment grade | Investments in Fixed Maturities      
Debt Securities, Available-for-sale [Line Items]      
Debt securities, available-for-sale, unrealized loss position, accumulated loss 708,000,000.0   875,300,000
Non-investment-grade | Investments in Fixed Maturities      
Debt Securities, Available-for-sale [Line Items]      
Debt securities, available-for-sale, unrealized loss position, accumulated loss $ 20,000,000.0   $ 14,200,000
Percentage of unrealized loss position to amortized cost basis of available for sale security average 4.40%   4.90%