Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021	Dec. 31, 2020
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 336.3	$ 330.6	[1]
Whole Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	22.3	20.9		$ 19.1	$ 17.8
Term Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	32.6	30.0		27.5	25.6
Experience life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	5.7	5.8		6.0	6.2
Limited-pay whole life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	7.4	6.7		5.6	4.4
Indexed Universal Life
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	16.8	15.4		13.7	12.9
Supplemental health
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	8.2	6.2		4.9	4.3
Total Annuities
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	214.0	221.1		$ 223.3	$ 223.1
Reconciling items
Deferred Policy Acquisition Cost [Line Items]
Deferred policy acquisition costs	$ 29.3	$ 24.5

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements