Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 347.2	$ 336.3
Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	23.8	22.3	$ 20.9	$ 19.1
Term Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	34.2	32.6	30.0	27.5
Experience life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	5.5	5.7	5.8	6.0
Limited-Pay Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	8.0	7.4	6.7	5.6
Indexed Universal Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	19.2	16.8	15.4	13.7
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	10.6	8.2	6.2	4.9
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	211.4	214.0	$ 221.1	$ 223.3
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 34.5	$ 29.3