Reinsurance (Schedule Of Trust Assets And Reinsurance Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 303.6	$ 255.6	$ 224.7
Restricted securities available for sale	[1]	58.6	46.1
Accounts payable and accrued liabilities		186.4	151.7
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		0.3	0.8
Restricted securities available for sale		58.6	46.1
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		43.3	34.1
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[2]	$ 1.6	$ 1.0

[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.