Investments - Realized Investment (Losses) Gains (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Gain (Loss) on Securities
Net investment gains (losses)	$ (15.5)	$ 4.9	$ (31.0)	$ (4.1)
Fixed maturity securities
Gain (Loss) on Securities
Net investment gains (losses)	(2.9)	1.5	(5.2)	(3.9)
Equity securities
Gain (Loss) on Securities
Net investment gains (losses)	(12.6)	4.4	(28.1)	1.7
Short-term investments and other
Gain (Loss) on Securities
Net investment gains (losses)	$ 0.0	$ (1.0)	$ 2.3	$ (1.9)