Long-Duration Insurance Contracts - Market Risk Benefits Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Market Risk Benefit [Roll Forward]
Balance, beginning of period	$ (6.2)	$ (3.6)	$ (3.9)	$ 0.2
Balance, beginning of period, before effects of changes in the instrument-specific credit risk	(6.8)	(3.2)	(4.5)	0.0
Changes in market risk benefits	0.3	(1.3)	(2.0)	(4.5)
Balance, end of period	(6.5)	(4.5)	(6.5)	(4.5)
Effect of changes in the instrument-specific credit risk	0.8	0.0	0.8	0.0
Balance, end of period	(5.7)	(4.5)	(5.7)	(4.5)
Net amount at risk	$ 15.1	$ 37.6	$ 15.1	$ 37.6
Weighted-average attained age of contract holders	62 years	63 years	62 years	63 years