Long-Duration Insurance Contracts - Reconciliation of Policyholder Account Balances to the Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 5,100.3	$ 5,187.0
Indexed Universal Life
Policyholder Account Balance [Line Items]
Policyholders' account balances	72.9	57.8	$ 47.6
Experience Life
Policyholder Account Balance [Line Items]
Policyholders' account balances	58.0	61.2	64.3
Fixed account annuity
Policyholder Account Balance [Line Items]
Policyholders' account balances	4,508.4	4,556.0	4,591.1
Indexed indexed account annuity
Policyholder Account Balance [Line Items]
Policyholders' account balances	409.5	449.0	510.3
SPIA (non-life contingent)
Policyholder Account Balance [Line Items]
Policyholders' account balances	28.6	32.6	$ 34.4
Reconciling items
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 22.9	$ 30.4