Investments - Realized Investment Gains (Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Gain (Loss) on Securities [Line Items]
Net investment losses	$ (56.5)	$ (11.0)	$ (2.3)
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Net investment losses	(29.1)	(7.7)	9.4
Equity securities
Gain (Loss) on Securities [Line Items]
Net investment losses	(32.6)	(0.8)	1.8
Short-term and other investments
Gain (Loss) on Securities [Line Items]
Net investment losses	$ 5.2	$ (2.5)	$ (13.5)