Fair Value Measurements - Carrying Values and Fair Value Estimates (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans to Policyholders	$ 279.8	$ 280.7
Short-Term Investments	545.3	1,037.1
Other Short-term Investments, Fair Value Disclosure	545.3	1,037.1
Mortgage Loans	103.1	75.3
Company-Owned Life Insurance	546.5	539.2
Equity Securities at Modified Cost	21.7	22.5
Fair Value Using NAV	21.7	22.5
Long-term debt	942.1	1,391.6
Long-term debt, fair value	841.7	1,278.4
Policyholder Obligations	632.0	637.7
Federal Home Loan Bank of Chicago
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Federal Home Loan Bank Borrowings, Fair Value Disclosure	536.2	541.3
Federal Home Loan Bank of Chicago \| United Insurance Company of America
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Policyholder Obligations	536.2	541.3
Loans to Policyholders
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	279.8	280.7
Mortgage Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	$ 103.1	$ 75.3

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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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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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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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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(8))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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