Fair Value Measurements - Carrying Values and Fair Value Estimates (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans to Policyholders	$ 280.3	$ 281.2
Short-Term Investments	696.9	520.9
Other Short-term Investments, Fair Value Disclosure	696.9	520.9
Mortgage Loans on Real Estate, Commercial and Consumer, Net	80.9	99.8
Company-Owned Life Insurance	533.0	513.5
Equity Securities at Modified Cost	22.1	32.6
Fair Value Using NAV	22.1	32.6
Long-Term Debt, Excluding Current Maturities	1,390.9
Long-term debt, fair value	1,298.3
Policyholder Obligations	618.3	655.7
Federal Home Loan Bank of Chicago
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Federal Home Loan Bank Borrowings, Fair Value Disclosure	521.3	557.4
Federal Home Loan Bank of Chicago \| United Insurance Company of America
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Policyholder Obligations	521.3	557.4
Consolidated Entity, Excluding VIE
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans to Policyholders	280.3	281.2
Company-Owned Life Insurance	533.0	513.5
Long-Term Debt, Excluding Current Maturities	941.0	1,389.2
Long-term Debt, Non-Current, at Amortized Cost, Fair Value	850.3	1,213.4
Policyholder Obligations	618.3	655.7
Loans To Policyholders [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	280.3	281.2
Mortgage Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	$ 80.9	$ 99.8

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Other Short-term Investments, Fair Value Disclosure

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Carrying value as of the balance sheet date of the sum of the obligations to contract holders to provide to them an agreed upon rate of return pursuant to the terms of the underlying contract. These contracts represent lending by the contract holders to the entity in return for a guaranteed (primarily fixed) interest rate until maturity, unless called earlier if the contracts provide that option to the contract holders (usually institutions). There is little or no insurance risk for the entity.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

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Amount before allowance of loans made to policy and contract holders using their life insurance contracts' cash value or separate accounts as collateral. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums over and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

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The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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