Long-Duration Insurance Contracts - Market Risk Benefits Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2020
Market Risk Benefit [Roll Forward]
Balance, beginning of period	$ 1.3	$ 4.0	$ 0.2	$ 4.8
Balance, beginning of period, before effects of changes in the instrument-specific credit risk	0.9	1.6	0.0	2.0
Changes in market risk benefits	(4.1)	2.6	(3.2)	2.2
Balance, end of period	(3.2)	4.2	(3.2)	4.2
Effect of changes in the instrument-specific credit risk	(0.4)	0.4	(0.4)	0.4
Balance, end of period	(3.6)	4.6	(3.6)	4.6
Net amount at risk	$ 28.1	$ 48.9	$ 28.1	$ 48.9	$ 8.6
Weighted-average attained age of contract holders	63 years	62 years	63 years	62 years