Long-Duration Insurance Contracts - Market Risk Benefits by Asset and Liability Balance (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Market Risk Benefit [Line Items]
Net	$ (6.3)	$ (3.9)	$ 1.3	$ 0.2
Deferred variable annuities
Market Risk Benefit [Line Items]
(Asset)	(8.3)	(6.7)
Liability	2.0	2.8
Net	$ (6.3)	$ (3.9)