Derivatives - Fair Value of Derivatives in Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Short-term and other investments	Short-term and other investments
Assets
Derivatives, reported in Short-term and other investments	$ 19.0	$ 6.8
FIA - embedded derivatives, reported in Policyholders' account balances
Liabilities
FIA - embedded derivatives, reported in Policyholders' account balances	86.3	91.0
IUL - embedded derivatives, reported in Policyholders' account balances
Liabilities
IUL - embedded derivatives, reported in Policyholders' account balances	$ 3.6	$ 1.2