Reinsurance (Schedule Of Trust Assets And Reinsurance Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 330.3	$ 303.6	$ 255.6
Restricted securities available for sale	[1]	59.3	58.6
Accounts payable and accrued liabilities		206.4	186.4
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		0.9	0.3
Restricted securities available for sale		59.3	58.6
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		44.1	43.3
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[2]	$ 1.8	$ 1.6

[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.