Long-Duration Insurance Contracts - Market Risk Benefits Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2020
Market Risk Benefit [Roll Forward]
Balance, beginning of year	$ 0.2	$ 4.8
Balance, beginning of year, before effects of changes in the instrument-specific credit risk	0.0	2.0
Changes in market risk benefits	0.9	(0.4)
Balance, end of period	0.9	1.6
Effect of changes in the instrument-specific credit risk	0.4	2.4
Balance, end of period	1.3	4.0
Net amount at risk	$ 38.3	$ 20.2	$ 8.6
Weighted-average attained age of contract holders	63 years	62 years