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, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Carrying Amount	[1]	$ 2,172.5	$ 2,224.5
Policy Loans		3,604.8	3,617.2
Long-term Debt		3,469.1	3,465.2
Liabilities, Fair Value Disclosure		286.5	255.7
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure		1,993.8	1,975.4
Mortgage Loans, Carrying Amount		2,172.5	2,224.5
Policy Loans, Fair Value Disclosure		3,673.5	3,672.9
Policy Loans		3,604.8	3,617.2
Miscellaneous Long-Term Investments, Fair Value Disclosure		35.4	26.9
Miscellaneous Long-Term Investments, Carrying Value		35.4	26.9
Financial Instruments, Financial Assets Fair Value Disclosure		5,702.7	5,675.2
Total Financial Instrument Assets Not Carried at Fair Value		5,812.7	5,868.6
Long-term Debt, Fair Value Disclosure		3,297.5	3,289.3
Long-term Debt		3,469.1	3,465.2
Unfunded Commitments		0.2	0.2
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure		525.5	324.2
Payables for Collateral on Investments		525.5	324.2
Liabilities, Fair Value Disclosure		3,823.2	3,613.7
Total Financial Instrument Liabilities Not Carried at Fair Value		3,994.8	3,789.6
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		2,589.5	3,246.1
Unfunded Commitments		0.0	0.0
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure		0.0	0.0
Liabilities, Fair Value Disclosure		2,589.5	3,246.1
Fair Value, Inputs, Level 2 | Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure		1,993.8	1,975.4
Policy Loans, Fair Value Disclosure		0.0	0.0
Miscellaneous Long-Term Investments, Fair Value Disclosure		35.2	26.7
Financial Instruments, Financial Assets Fair Value Disclosure		2,029.0	2,002.1
Long-term Debt, Fair Value Disclosure		708.0	43.2
Unfunded Commitments		0.2	0.2
Federal Home Loan Bank Funding Agreements, Fair Value Disclosure		525.5	324.2
Liabilities, Fair Value Disclosure		1,233.7	367.6
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		3,673.5	3,672.9
Miscellaneous Long-Term Investments, Fair Value Disclosure		0.2	0.2
Financial Instruments, Financial Assets Fair Value Disclosure		3,673.7	3,673.1
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

[1] 1Loan-to-Value Ratio utilizes the most recent internal valuation of the property