Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 351.4		$ 347.2
Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	24.6	$ 24.1	23.8	$ 23.0	$ 22.6	$ 22.3
Term Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	34.8	34.5	34.2	33.5	32.9	32.6
Experience life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	5.4	5.4	5.5	5.6	5.7	5.7
Limited-Pay Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	8.1	8.0	8.0	7.7	7.5	7.4
Indexed Universal Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	20.3	19.8	19.2	17.8	17.1	16.8
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	12.1	11.2	10.6	9.3	8.7	8.2
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	209.4	$ 210.4	211.4	$ 212.4	$ 212.9	$ 214.0
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 36.7		$ 34.5