Fair Value of Financial Instruments - Financial Instrument Not Carried at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Level 1
Financial Assets
Other investments	$ 0.0	$ 0.0
Deposit asset on reinsurance	0.0	0.0
Financial Liabilities
Policyholders' account balances	0.0	0.0
Other policyholder funds	0.0	0.0
Reverse repurchase agreement	0.0
Long-term debt	0.0	0.0
Level 2
Financial Assets
Other investments	37.0	33.8
Deposit asset on reinsurance	0.0	0.0
Financial Liabilities
Policyholders' account balances	0.0	0.0
Other policyholder funds	992.9	908.7
Reverse repurchase agreement	12.4
Long-term debt	575.1	571.4
Level 3
Financial Assets
Other investments	187.3	187.9
Deposit asset on reinsurance	2,121.9	2,259.6
Financial Liabilities
Policyholders' account balances	4,710.1	4,861.8
Other policyholder funds	2.8	7.3
Reverse repurchase agreement	0.0
Long-term debt	0.0	0.0
Carrying Value
Financial Assets
Other investments	221.0	218.4
Deposit asset on reinsurance	2,434.3	2,496.6
Financial Liabilities
Policyholders' account balances	5,020.2	4,996.3
Other policyholder funds	995.7	916.0
Reverse repurchase agreement	12.0
Long-term debt	547.0	546.0
Fair Value
Financial Assets
Other investments	224.3	221.7
Deposit asset on reinsurance	2,121.9	2,259.6
Financial Liabilities
Policyholders' account balances	4,710.1	4,861.8
Other policyholder funds	995.7	916.0
Reverse repurchase agreement	12.4
Long-term debt	$ 575.1	$ 571.4