Investment Securities - Schedule of Interest Income on Fixed Maturity Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Schedule of Investments [Line Items]
Total investment income	$ 21.0	$ 21.0
Third-party investment expenses	(0.4)	(0.4)
Net investment income	20.6	20.6
Fixed maturity investments
Schedule of Investments [Line Items]
Total investment income	8.2	6.5
Short-term investments
Schedule of Investments [Line Items]
Total investment income	0.1	1.6
Other long-term investments
Schedule of Investments [Line Items]
Total investment income	13.2	13.8
TPC Providers
Schedule of Investments [Line Items]
Total investment income	$ 0.5	$ 0.9