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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% |

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