Long-Duration Insurance Contracts - Market Risk Benefits by Asset and Liability Balance (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Market Risk Benefit [Line Items]
Net	$ (5.7)	$ (6.2)	$ (3.9)	$ (4.5)	$ (3.6)	$ 0.2
Deferred variable annuities
Market Risk Benefit [Line Items]
(Asset)	(8.5)		(6.7)
Liability	2.9		2.8
Net	$ (5.7)		$ (3.9)