Reinsurance (Schedule Of Trust Assets And Reinsurance Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 380.2	$ 330.3	$ 303.6
Restricted securities available for sale	[1]	66.1	59.3
Accounts payable and accrued liabilities		186.7	206.4
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		0.7	0.9
Restricted securities available for sale		66.1	59.3
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		48.5	44.1
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[2]	$ 2.3	$ 1.8

[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.