Long-Duration Insurance Contracts - Reconciliation of Policyholder Account Balances to the Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 5,056.1	$ 5,064.1
Indexed Universal Life
Policyholder Account Balance [Line Items]
Policyholders' account balances	100.6	95.5	$ 78.2	$ 72.9
Experience life
Policyholder Account Balance [Line Items]
Policyholders' account balances	53.7	54.8	57.4	58.0
Fixed Account Annuities
Policyholder Account Balance [Line Items]
Policyholders' account balances	4,482.6	4,486.8	4,495.9	4,508.4
Fixed Indexed Account Annuities
Policyholder Account Balance [Line Items]
Policyholders' account balances	365.1	373.3	399.7	409.5
SPIA (non-life contingent)
Policyholder Account Balance [Line Items]
Policyholders' account balances	26.2	26.1	$ 28.3	$ 28.6
Reconciling items
Policyholder Account Balance [Line Items]
Policyholders' account balances	$ 27.9	$ 27.6