Reinsurance (Schedule of Trust Assets and Reinsurance Liabilities) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 538.5	$ 380.2	$ 408.1	$ 330.3
Restricted securities available for sale	[1]	68.1	66.1
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		0.5	0.7
Restricted securities available for sale		68.1	66.1
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		52.8	48.5
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[2]	$ 2.3	$ 2.3

[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.