Fair Value Measurements - Carrying Values and Fair Value Estimates (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans to Policyholders	$ 279.3	$ 280.7
Short-Term Investments	371.2	1,037.1
Other Short-term Investments, Fair Value Disclosure	371.2	1,037.1
Mortgage Loans	148.2	75.3
Company-Owned Life Insurance	567.9	539.2
Equity Securities at Modified Cost	22.2	22.5
Fair Value Using NAV	22.2	22.5
Long-term debt	943.1	1,391.6
Long-term debt, fair value	864.6	1,278.4
Policyholder Obligations	620.0	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	525.2	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	525.2	541.3
Loans to Policyholders
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	279.3	280.7
Mortgage Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	$ 148.2	$ 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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- 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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