Long-Duration Insurance Contracts - Market Risk Benefits Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Market Risk Benefit [Roll Forward]
Balance, beginning of period	$ (6.3)	$ 1.3	$ (3.9)	$ 0.2
Balance, beginning of period, before effects of changes in the instrument-specific credit risk	(6.8)	0.9	(4.5)	0.0
Changes in market risk benefits	0.0	(4.1)	(2.3)	(3.2)
Balance, end of period	(6.8)	(3.2)	(6.8)	(3.2)
Effect of changes in the instrument-specific credit risk	0.6	(0.4)	0.6	(0.4)
Balance, end of period	(6.2)	(3.6)	(6.2)	(3.6)
Net amount at risk	$ 16.5	$ 28.1	$ 16.5	$ 28.1
Weighted-average attained age of contract holders	63 years	63 years	62 years	63 years