Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 345.4		$ 336.3
Whole Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	23.4	$ 23.0	22.3
Term Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	33.8	33.5	32.6
Experience Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	5.6	5.6	5.7
Limited Pay Whole Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	7.8	7.7	7.4
Indexed Universal Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	18.3	17.8	16.8
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	9.9	9.3	8.2
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	212.0	$ 212.4	214.0
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 34.6		$ 29.3