Fair Values of Financial Instruments Carrying Amounts and Estimated Fair value of Financial Instruments Not Measured at Fair Value (Details) - USD ($) $ in Millions		Sep. 30, 2026	Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans (net of allowance for credit losses of $16.4; $15.9)	[1]	$ 2,053.2	$ 2,109.5
Policy Loans		3,538.1	3,668.1
Miscellaneous Long-Term Investments, Carrying Value		50.4	40.9
Total Financial Instrument Assets Not Carried at Fair Value		5,641.7	5,818.5
Liabilities Related to Investment Contracts, Fair Value Disclosure		994.7
Long-term Debt		3,765.7	3,767.6
Other Liabilities		2,937.2	2,995.8
Other Liabilities, Carrying Value		311.8	644.0
Liabilities, Fair Value Disclosure		421.5	269.7
Total Financial Instrument Liabilities Not Carried at Fair Value		5,072.2	4,411.6
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure		1,839.8	1,965.1
Policy Loans, Fair Value Disclosure		3,581.5	3,739.5
Miscellaneous Long-Term Investments, Fair Value Disclosure		50.4	40.9
Financial Instruments, Financial Assets Fair Value Disclosure		5,471.7	5,745.5
Liabilities Related to Investment Contracts, Fair Value Disclosure		994.7
Long-term Debt, Fair Value Disclosure		3,350.6	3,641.4
Other Liabilities		311.8	644.0
Liabilities, Fair Value Disclosure		4,657.1	4,285.4
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
Liabilities Related to Investment Contracts, Fair Value Disclosure		0.0
Long-term Debt, Fair Value Disclosure		3,331.9	2,548.2
Other Liabilities		0.0	0.0
Liabilities, Fair Value Disclosure		3,331.9	2,548.2
Fair Value, Inputs, Level 2 | Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Mortgage Loans, Fair Value Disclosure		1,839.8	1,965.1
Policy Loans, Fair Value Disclosure		0.0	0.0
Miscellaneous Long-Term Investments, Fair Value Disclosure		50.4	40.7
Financial Instruments, Financial Assets Fair Value Disclosure		1,890.2	2,005.8
Liabilities Related to Investment Contracts, Fair Value Disclosure		994.7
Long-term Debt, Fair Value Disclosure		18.7	1,093.2
Other Liabilities		311.8	644.0
Liabilities, Fair Value Disclosure		1,325.2	1,737.2
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		3,581.5	3,739.5
Miscellaneous Long-Term Investments, Fair Value Disclosure		0.0	0.2
Financial Instruments, Financial Assets Fair Value Disclosure		3,581.5	3,739.7
Liabilities Related to Investment Contracts, Fair Value Disclosure		0.0
Long-term Debt, Fair Value Disclosure		0.0	0.0
Other Liabilities		0.0	0.0
Liabilities, Fair Value Disclosure		$ 0.0	$ 0.0

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