Reinsurance (Schedule of Trust Assets and Reinsurance Liabilities) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 391.9	$ 330.3	$ 329.8	$ 303.6
Restricted securities available for sale	[1]	66.8	59.3
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		1.0	0.9
Restricted securities available for sale		66.8	59.3
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		51.2	44.1
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[2]	$ 2.6	$ 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.