Investments (Schedule of Pre-tax Net Realized and Unrealized Gains (Losses) on Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Net gains (losses) recognized during the period	$ (29.1)	$ 0.3	$ (106.1)	$ 65.9
Less: net gains (losses) recognized on equity securities sold during the period	(0.1)	0.9	(8.8)	1.4
Net unrealized gains (losses) recognized during the period on equity securities still held	$ (29.0)	$ (0.6)	$ (97.3)	$ 64.5