Investments - Net Investment Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ 3.3	$ 3.8	$ (5.9)	$ 0.1
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	(0.6)	(0.3)	(4.5)	(3.6)
Equity securities
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	2.2	5.1	0.2	5.6
Short-term investments and other
Gain (Loss) on Securities [Line Items]
Net investment gains (losses)	$ 1.7	$ (1.0)	$ (1.6)	$ (1.9)