Investments - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date	$ 1,624,400,000
Financing Receivable, Accrued Interest, before Allowance for Credit Loss	72,100,000		$ 77,000,000.0
Equity securities, FV-NI, unrealized gain (loss)	$ (2,300,000)	$ 5,100,000
Percentage of Equity Method Limited Liability Investments reported with a lag	3.20%
Percentage of Equity Method Limited Liability Investments reported with a One Month Lag	4.30%
Loans to Policyholders	$ 280,300,000		281,200,000
Equity Securities at Modified Cost	22,100,000		32,600,000
Equity securities without readily determinable fair value, impairment loss, cumulative amount	4,900,000		8,000,000.0
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Equity securities without readily determinable fair value, impairment loss, annual amount	(400,000)	$ 0
Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Other Receivables	6,000,000.0		900,000
Other liabilities	13,800,000		0
Debt securities, available-for-sale, unrealized loss position, accumulated loss	632,700,000		730,300,000
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	223,500,000
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	109,900,000
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	82,800,000
Other Non-Governmental Issuers
Debt Securities, Available-for-sale [Line Items]
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date	1,208,200,000
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Other Receivables	8,000,000.0		100,000
Other liabilities	0		0
Equity Method Investments
Debt Securities, Available-for-sale [Line Items]
Other Receivables	0		0
Other liabilities	0		0
Consolidated Entity, Excluding VIE
Debt Securities, Available-for-sale [Line Items]
Other Receivables	202,100,000		200,500,000
Equity securities	228,300,000		225,800,000
Loans to Policyholders	280,300,000		281,200,000
Consolidated Entity, Excluding VIE | Equity Method Limited Liability Investments
Debt Securities, Available-for-sale [Line Items]
Equity Method Investments	202,600,000		221,700,000
Consolidated Entity, Excluding VIE | Alternative Energy Partnership Investments
Debt Securities, Available-for-sale [Line Items]
Equity Method Investments	17,400,000		17,300,000
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	77,000,000.0
Investment grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	617,700,000		704,800,000
Non-investment-grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	$ 15,000,000.0		$ 25,500,000
Percentage of unrealized loss position to amortized cost basis of available for sale security average	4.60%		8.80%