Fair Values of Financial Instruments Carrying Amounts and Estimated Fair Value of Financial Instruments Not Measured at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage Loans, Fair Value Disclosure	$ 2,201.6	$ 2,306.2
Mortgage Loans	2,190.6	2,213.2
Policy Loans, Fair Value Disclosure	3,639.4	3,677.5
Policy Loans	3,545.4	3,571.1
Miscellaneous Long-Term Investments. Fair Value Disclosure	142.1	162.3
Financial Instruments, Financial Assets Fair Value Disclosure	5,983.1	6,146.0
Long-term Debt, Fair Value Disclosure	3,146.2	3,048.7
Long-term Debt	2,997.7	2,738.4
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	272.0	350.0
Unfunded Commitments	3.7	3.7
Liabilities, Fair Value Disclosure	3,421.9	3,402.4
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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	2,642.6	1,171.8
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	0.0	0.0
Unfunded Commitments	0.0	0.0
Liabilities, Fair Value Disclosure	2,642.6	1,171.8
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage Loans, Fair Value Disclosure	2,201.6	2,306.2
Policy Loans, Fair Value Disclosure	0.0	0.0
Miscellaneous Long-Term Investments. Fair Value Disclosure	32.1	34.1
Financial Instruments, Financial Assets Fair Value Disclosure	2,233.7	2,340.3
Long-term Debt, Fair Value Disclosure	503.6	1,876.9
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	272.0	350.0
Unfunded Commitments	3.7	3.7
Liabilities, Fair Value Disclosure	779.3	2,230.6
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage Loans, Fair Value Disclosure	0.0	0.0
Policy Loans, Fair Value Disclosure	3,639.4	3,677.5
Miscellaneous Long-Term Investments. Fair Value Disclosure	110.0	128.2
Financial Instruments, Financial Assets Fair Value Disclosure	3,749.4	3,805.7
Long-term Debt, Fair Value Disclosure	0.0	0.0
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure	0.0	0.0
Unfunded Commitments	0.0	0.0
Liabilities, Fair Value Disclosure	0.0	0.0
Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage Loans	2,190.6	2,213.2
Policy Loans	3,545.4	3,571.1
Miscellaneous Long-Term Investments	142.1	162.3
Total Financial Instrument Assets Not Carried at Fair Value	5,878.1	5,946.6
Long-term Debt	2,997.7	2,738.4
Federal Home Loan Bank Funding Agreements	272.0	350.0
Unfunded Commitments	3.7	3.7
Total Financial Instrument Liabilities Not Carried at Fair Value	$ 3,273.4	$ 3,092.1

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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Miscellaneous Long-Term Investments, Carrying Value

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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 capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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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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