Long-Duration Insurance Contracts - Market Risk Benefits by Asset and Liability Balance (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Market Risk Benefit [Line Items]
Net	$ (3.9)	$ 0.3	$ 4.8	$ 8.6
Deferred variable annuities
Market Risk Benefit [Line Items]
(Asset)	(6.7)	(4.4)
Liability	2.8	4.7
Net	$ (3.9)	$ 0.3