Long-Duration Insurance Contracts - Market Risk Benefits Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020
Market Risk Benefit [Roll Forward]
Balance, beginning of period	$ 0.3	$ 4.8
Balance, beginning of period, before effects of changes in the instrument-specific credit risk	0.0	2.0
Changes in market risk benefits	(4.5)	(2.0)
Balance, end of period	(4.5)	0.0
Effect of changes in the instrument-specific credit risk	0.6	0.3
Balance, end of period	(3.9)	0.3
Net amount at risk	$ 20.5	$ 55.3	$ 8.6
Weighted-average attained age of contract holders	62 years	61 years