Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 341.5		$ 336.3
Whole Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	23.0	$ 22.6	22.3
Term Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	33.5	32.9	32.6
Experience Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	5.6	5.7	5.7
Limited Pay Whole Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	7.7	7.5	7.4
Indexed Universal Life Insurance
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	17.8	17.1	16.8
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	9.3	8.7	8.2
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	212.4	$ 212.9	214.0
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 32.2		$ 29.3