Investments - Net Investment Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Gain (Loss) on Securities
Net investment losses	$ (12.8)	$ (6.5)	$ (43.8)	$ (10.6)
Fixed maturity securities
Gain (Loss) on Securities
Net investment losses	(10.7)	(4.0)	(15.9)	(7.9)
Equity securities
Gain (Loss) on Securities
Net investment losses	(4.4)	(1.0)	(32.5)	0.7
Short-term investments and other
Gain (Loss) on Securities
Net investment losses	$ 2.3	$ (1.5)	$ 4.6	$ (3.4)