Investment Income and Gains and Losses (Schedule of Allowance for Credit Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Allowance for credit losses as of the beginning of the period	$ 3.2	$ 7.1
Additional credit losses on investments for which an allowance was previously recognized	6.9	0.2
Reductions for disposals	(0.1)	(2.1)
Recoveries		(2.0)
Allowance for credit losses as of the end of the period	$ 10.0	$ 3.2