Reinsurance (Schedule Of Trust Assets And Reinsurance Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 457.7	$ 410.0	$ 410.9
Debt Securities, Available-for-sale, Restricted	[1]	93.2	72.3
Accounts payable and accrued liabilities		318.8	260.8
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		1.4	0.4
Debt Securities, Available-for-sale, Restricted		93.2	72.3
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		67.6	54.4
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[2]	$ 5.6	$ 3.1

[1] Measured at fair value on a recurring basis.

[2] The claims reserve represents our liability for incurred-but-not-reported claims and is estimated based on historical claims experience.