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, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Carrying Amount	$ 2,402.2	$ 2,432.1
Policy Loans	3,628.8	3,683.9
Long-term Debt	3,346.8	3,345.7
Unfunded Commitments	0.9
Liabilities, Fair Value Disclosure	77.8	99.5
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure	2,456.1	2,641.8
Mortgage Loans, Carrying Amount	2,402.2	2,432.1
Policy Loans, Fair Value Disclosure	3,761.3	3,850.8
Policy Loans	3,628.8	3,683.9
Miscellaneous Long-Term Investments, Fair Value Disclosure	51.3	57.5
Miscellaneous Long-Term Investments	51.3	57.5
Financial Instruments, Financial Assets Fair Value Disclosure	6,268.7	6,550.1
Total Financial Instrument Assets Not Carried at Fair Value	6,082.3	6,173.5
Long-term Debt, Fair Value Disclosure	3,788.8	3,887.4
Long-term Debt	3,346.8	3,345.7
Advances, Fair Value Disclosure	302.2	312.2
Federal Home Loan Bank Funding Agreements	302.2	312.2
Unfunded Commitments	0.9	0.9
Liabilities, Fair Value Disclosure	4,091.9	4,200.5
Total Financial Instrument Liabilities Not Carried at Fair Value	3,649.9	3,658.8
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	3,230.9	2,393.1
Advances, Fair Value Disclosure	0.0	0.0
Unfunded Commitments	0.0	0.0
Liabilities, Fair Value Disclosure	3,230.9	2,393.1
Fair Value, Inputs, Level 2 \| Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure	2,456.1	2,641.8
Policy Loans, Fair Value Disclosure	0.0	0.0
Miscellaneous Long-Term Investments, Fair Value Disclosure	26.9	28.2
Financial Instruments, Financial Assets Fair Value Disclosure	2,483.0	2,670.0
Long-term Debt, Fair Value Disclosure	557.9	1,494.3
Advances, Fair Value Disclosure	302.2	312.2
Unfunded Commitments	0.9	0.9
Liabilities, Fair Value Disclosure	861.0	1,807.4
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	3,761.3	3,850.8
Miscellaneous Long-Term Investments, Fair Value Disclosure	24.4	29.3
Financial Instruments, Financial Assets Fair Value Disclosure	3,785.7	3,880.1
Long-term Debt, Fair Value Disclosure	0.0	0.0
Advances, Fair Value Disclosure	0.0	0.0
Unfunded Commitments	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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Fair value of Federal Home Loan Bank (FHLBank) advances carried under the fair value option.

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

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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 or contingent commitments to qualified affordable housing project investments.

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