Investments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 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	$ 1,699.5		$ 1,699.5
Fixed maturities, allowance for credit losses	(7.1)	$ 13.6	(7.1)	$ 13.6	$ (9.6)	$ 7.5
Equity securities	247.0		247.0		243.2
Equity securities, FV-NI, unrealized gain (loss)	9.8
Equity securities without readily determinable fair value, impairment loss, cumulative amount	9.6		9.6
Other Receivables	262.0		262.0		262.6
Equity Securities, FV-NI, Current	$ 247.0		$ 247.0		243.2
Percentage of Equity Method Limited Liability Investments reported with a lag	2.00%		2.00%
Percentage of Equity Method Limited Liability Investments reported with a One Month Lag	5.30%		5.30%
Company-Owned Life Insurance	$ 500.5		$ 500.5		586.5
Loans to Policyholders	281.6		281.6
Loans to Policyholders	281.6		281.6		283.4
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	248.1		248.1
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	94.1		94.1
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	65.4		65.4
Other Non-Governmental Issuers
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	1,291.9		1,291.9
Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	857.2		857.2		936.8
12 Months or Longer	783.4		783.4		308.9
Other Receivables	12.5		12.5		5.8
Other liabilities	2.7		2.7		25.9
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Other Receivables	31.3		31.3		0.0
Equity Securities | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	247.0		247.0		243.2
Equity Securities, FV-NI, Current	247.0		247.0		243.2
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	8.3		8.3		13.4
Equity Securities, FV-NI, Current	8.3		8.3		13.4
Preferred Stocks | Other Industries | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	11.3		11.3		10.8
Equity Securities, FV-NI, Current	11.3		11.3		10.8
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		0.0		0.0
Equity Securities, FV-NI, Current	0.0		0.0		0.0
Common Stock | Other Industries | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	0.8		0.8		1.2
Equity Securities, FV-NI, Current	0.8		0.8		1.2
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	0.4		0.4		0.3
Equity Securities, FV-NI, Current	0.4		0.4		0.3
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	465.6		465.6		499.7
12 Months or Longer	406.3		406.3		125.8
Fixed maturities, allowance for credit losses	(6.7)	13.6	(6.7)	13.6	(8.9)	$ 7.5
Equity Method Investments
Debt Securities, Available-for-sale [Line Items]
Other Receivables	0.8		0.8		35.2
Other liabilities	0.0		0.0
Variable Interest Entity, Not Primary Beneficiary
Debt Securities, Available-for-sale [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	16.8		16.8		16.3
Variable Interest Entity, Funding Investment Commitment, Funding	0.0	$ 0.0	0.0	$ 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	90.5		90.5
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		0.0		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	827.1		827.1		904.0
Non-investment-grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	$ 30.1		$ 30.1		$ 32.8
Percentage of unrealized loss position to amortized cost basis of available for sale security average	9.50%		9.50%		11.00%