Investments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	$ 1,712,000,000
Fixed maturities, allowance for credit losses	(7,400,000)	$ 9,100,000	$ (9,600,000)	$ 7,500,000
Equity securities	243,600,000		243,200,000
Equity securities, FV-NI, unrealized gain (loss)	4,400,000
Equity securities without readily determinable fair value, impairment loss, cumulative amount	9,600,000
Other Receivables	249,400,000		262,600,000
Equity Securities, FV-NI, Current	$ 243,600,000		243,200,000
Percentage of Equity Method Limited Liability Investments reported with a lag	2.00%
Percentage of Equity Method Limited Liability Investments reported with a One Month Lag	5.60%
Company-Owned Life Insurance	$ 595,300,000		586,500,000
Loans to Policyholders	283,100,000
Loans to Policyholders	283,100,000		283,400,000
Government National Mortgage Association Certificates and Obligations (GNMA)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	259,600,000
Federal National Mortgage Association Certificates and Obligations (FNMA)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	97,500,000
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	67,900,000
Other Non-Governmental Issuers
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	1,287,000,000
Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	785,100,000		936,800,000
12 Months or Longer	606,800,000		308,900,000
Other Receivables	11,400,000		5,800,000
Other liabilities	3,700,000		25,900,000
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Other Receivables	0
Other liabilities		0
Equity Securities | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	243,600,000		243,200,000
Equity Securities, FV-NI, Current	243,600,000		243,200,000
Equity Securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	7,600,000		13,400,000
Equity Securities, FV-NI, Current	7,600,000		13,400,000
Preferred Stocks | Other Industries | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	11,200,000		10,800,000
Equity Securities, FV-NI, Current	11,200,000		10,800,000
Preferred Stocks | Other Industries | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	0		0
Equity Securities, FV-NI, Current	0		0
Common Stock | Other Industries | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	600,000		1,200,000
Equity Securities, FV-NI, Current	600,000		1,200,000
Common Stock | Other Industries | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	200,000		300,000
Equity Securities, FV-NI, Current	200,000		300,000
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	418,500,000		499,700,000
12 Months or Longer	285,600,000		125,800,000
Fixed maturities, allowance for credit losses	(6,600,000)	9,100,000	(8,900,000)	$ 7,500,000
Equity Method Investments
Debt Securities, Available-for-sale [Line Items]
Other Receivables	29,900,000		35,200,000
Other liabilities	0
Variable Interest Entity, Not Primary Beneficiary
Debt Securities, Available-for-sale [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	17,000,000		16,300,000
Variable Interest Entity, Funding Investment Commitment, Funding	0	$ 0
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	96,400,000
Variable Interest Entity, Not Primary Beneficiary | Alternative Energy Partnership Investments
Debt Securities, Available-for-sale [Line Items]
Outstanding commitments to fund equity method limited liability investments	$ 0		0
Investment-grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss			904,000,000
Non-investment-grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss			$ 32,800,000
Percentage of unrealized loss position to amortized cost basis of available for sale security average	11.30%		11.00%