Fair Values of Financial Instruments Carrying Amounts and Estimated Fair value of Financial Instruments Not Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Carrying Amount	$ 2,298.8	$ 2,318.2
Policy Loans	3,579.1	3,620.2
Long-term Debt	3,431.0	3,430.4
Liabilities, Fair Value Disclosure	147.0	117.7
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure	2,021.9	2,070.7
Mortgage Loans, Carrying Amount	2,298.8	2,318.2
Policy Loans, Fair Value Disclosure	3,650.2	3,696.3
Policy Loans	3,579.1	3,620.2
Miscellaneous Long-Term Investments, Fair Value Disclosure	17.9	16.0
Miscellaneous Long-Term Investments	17.9	16.0
Financial Instruments, Financial Assets Fair Value Disclosure	5,690.0	5,783.0
Total Financial Instrument Assets Not Carried at Fair Value	5,895.8	5,954.4
Long-term Debt, Fair Value Disclosure	3,230.7	3,227.9
Long-term Debt	3,431.0	3,430.4
Unfunded Commitments	0.2	0.2
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	108.2	64.5
Federal Home Loan Bank Funding Agreements	108.2	64.5
Liabilities, Fair Value Disclosure	3,339.1	3,292.6
Total Financial Instrument Liabilities Not Carried at Fair Value	3,539.4	3,495.1
Fair Value, Inputs, Level 1 \| Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure	0.0	0.0
Policy Loans, Fair Value Disclosure	0.0	0.0
Miscellaneous Long-Term Investments, Fair Value Disclosure	0.0	0.0
Financial Instruments, Financial Assets Fair Value Disclosure	0.0	0.0
Long-term Debt, Fair Value Disclosure	2,628.1	2,629.1
Unfunded Commitments	0.0	0.0
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	0.0	0.0
Liabilities, Fair Value Disclosure	2,628.1	2,629.1
Fair Value, Inputs, Level 2 \| Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure	2,021.9	2,070.7
Policy Loans, Fair Value Disclosure	0.0	0.0
Miscellaneous Long-Term Investments, Fair Value Disclosure	17.6	15.7
Financial Instruments, Financial Assets Fair Value Disclosure	2,039.5	2,086.4
Long-term Debt, Fair Value Disclosure	602.6	598.8
Unfunded Commitments	0.2	0.2
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	108.2	64.5
Liabilities, Fair Value Disclosure	711.0	663.5
Fair Value, Inputs, Level 3 \| Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure	0.0	0.0
Policy Loans, Fair Value Disclosure	3,650.2	3,696.3
Miscellaneous Long-Term Investments, Fair Value Disclosure	0.3	0.3
Financial Instruments, Financial Assets Fair Value Disclosure	3,650.5	3,696.6
Long-term Debt, Fair Value Disclosure	0.0	0.0
Unfunded Commitments	0.0	0.0
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	0.0	0.0
Liabilities, Fair Value Disclosure	$ 0.0	$ 0.0

Financial Instruments, Financial Assets Fair Value Disclosure, Carrying Value

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Financial Instruments, Financial Assets Fair Value Disclosure, Total

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Miscellaneous Long-Term Investments

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Total Financial Instrument Liabilities Not Carried at Fair Value

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Amount of Federal Home Loan Bank (FHLBank) advances to member financial institutions.

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

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Fair value of financial and nonfinancial obligations.

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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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Amount of long-term debt and lease obligation, classified as noncurrent.

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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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Fair value portion of mortgage loans held-for-sale.

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Fair value portion of notes payable.

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Amount of commitment and contingent commitment, including amount of delayed equity contribution, for investment that generates income tax credit and other income tax benefit under tax credit program elected to be accounted for using proportional amortization method. Includes, but is not limited to, commitment and contingent commitment related to investment under tax credit program not meeting condition for accounting under proportional amortization method.

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