Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 358.3		$ 347.2
Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	24.8	$ 24.6	23.8	$ 23.4	$ 23.0	$ 22.3
Term Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	35.3	34.8	34.2	33.8	33.5	32.6
Experience life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	5.3	5.4	5.5	5.6	5.6	5.7
Limited-Pay Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	8.2	8.1	8.0	7.8	7.7	7.4
Indexed Universal Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	21.4	20.3	19.2	18.3	17.8	16.8
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	12.8	12.1	10.6	9.9	9.3	8.2
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	208.8	$ 209.4	211.4	$ 212.0	$ 212.4	$ 214.0
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 41.7		$ 34.5