Investments - Realized Investment (Losses) Gains (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Gain (Loss) on Securities
Net investment losses	$ (15.5)	$ (9.0)
Fixed maturity securities
Gain (Loss) on Securities
Net investment losses	(2.3)	(5.4)
Equity securities
Gain (Loss) on Securities
Net investment losses	(15.5)	(2.7)
Short-term investments and other
Gain (Loss) on Securities
Net investment losses	$ 2.3	$ (0.9)