Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2026	Jun. 30, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 360.1		$ 358.2
Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	25.7	$ 25.5	24.9	$ 24.8	$ 24.6	$ 23.8
Term Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	36.0	36.0	35.5	35.3	34.8	34.2
Experience life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	4.9	5.0	5.2	5.3	5.4	5.5
Limited-Pay Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	8.4	8.4	8.3	8.2	8.1	8.0
Indexed Universal Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	26.1	24.9	22.8	21.4	20.3	19.2
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	16.5	15.6	13.7	12.8	12.1	10.6
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	204.4	$ 205.3	207.7	$ 208.8	$ 209.4	$ 211.4
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 38.1		$ 40.1