Long-Duration Insurance Contracts - Market Risk Benefits Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Market Risk Benefit [Roll Forward]
Balance, beginning of period	$ (3.9)	$ 0.2
Balance, beginning of period, before effects of changes in the instrument-specific credit risk	(4.5)	0.0
Changes in market risk benefits	(2.3)	0.9
Balance, end of period	(6.8)	0.9
Effect of changes in the instrument-specific credit risk	0.5	0.4
Balance, end of period	(6.3)	1.3
Net amount at risk	$ 16.6	$ 38.3
Weighted-average attained age of contract holders	62 years	63 years