Investments - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	$ 1,643,700,000		$ 1,643,700,000
Fixed maturities, allowance for credit losses	(7,500,000)	$ 4,400,000	(7,500,000)	$ 4,400,000	$ (7,500,000)	$ 3,300,000
Equity securities	322,700,000		322,700,000		830,600,000
Equity securities, FV-NI, unrealized gain (loss)	(24,400,000)
Equity securities without readily determinable fair value, impairment loss, cumulative amount	9,600,000		9,600,000
Other Receivables	228,700,000		228,700,000		207,300,000
Equity Securities, FV-NI, Current	$ 322,700,000		$ 322,700,000		830,600,000
Percentage of Equity Method Limited Liability Investments reported with a lag	4.70%		4.70%
Percentage of Equity Method Limited Liability Investments reported with a One Month Lag	0.20%		0.20%
Company-Owned Life Insurance	$ 578,600,000		$ 578,600,000		448,100,000
Loans to Policyholders	283,900,000		283,900,000
Loans to Policyholders	283,200,000		283,200,000		286,200,000
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	251,400,000		251,400,000
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	77,000,000		77,000,000
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	68,300,000		68,300,000
Other Non-Governmental Issuers
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value	1,247,000,000		1,247,000,000
Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	1,031,300,000		1,031,300,000		32,700,000
12 Months or Longer	151,500,000		151,500,000		5,900,000
Other Receivables	5,700,000		5,700,000		600,000
Other liabilities	7,600,000		7,600,000		12,700,000
Equity Securities
Debt Securities, Available-for-sale [Line Items]
Other Receivables	0		0
Other liabilities		2,700,000		2,700,000
Equity Securities | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	322,700,000		322,700,000		830,600,000
Equity Securities, FV-NI, Current	322,700,000		322,700,000		830,600,000
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	71,800,000		71,800,000		453,800,000
Equity Securities, FV-NI, Current	71,800,000		71,800,000		453,800,000
Preferred Stocks | Other Industries | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	11,700,000		11,700,000		17,600,000
Equity Securities, FV-NI, Current	11,700,000		11,700,000		17,600,000
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		0
Equity Securities, FV-NI, Current	0		0		0
Common Stock | Other Industries | Fair Value, Measurements, Recurring
Debt Securities, Available-for-sale [Line Items]
Equity securities	1,100,000		1,100,000		2,900,000
Equity Securities, FV-NI, Current	1,100,000		1,100,000		2,900,000
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		200,000		2,900,000
Equity Securities, FV-NI, Current	200,000		200,000		2,900,000
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	575,800,000		575,800,000		16,000,000.0
12 Months or Longer	68,600,000		68,600,000		2,900,000
Fixed maturities, allowance for credit losses	(7,100,000)	4,400,000	(7,100,000)	4,400,000	(7,500,000)	$ 3,000,000.0
Equity Method Investments
Debt Securities, Available-for-sale [Line Items]
Other Receivables	27,800,000		27,800,000		1,200,000
Other liabilities	1,000,000		1,000,000		0
Variable Interest Entity, Not Primary Beneficiary
Debt Securities, Available-for-sale [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	16,900,000		16,900,000		39,600,000
Variable Interest Entity, Funding Investment Commitment, Funding	0	$ 31,500,000	0	$ 80,000,000.0
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	83,700,000		83,700,000
Investment-grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	998,200,000		998,200,000		23,700,000
Non-investment-grade | Investments in Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, unrealized loss position, accumulated loss	$ 33,100,000		$ 33,100,000		$ 9,000,000
Percentage of unrealized loss position to amortized cost basis of available for sale security average	11.00%		11.00%		4.00%