Reinsurance (Schedule of Trust Assets and Reinsurance Liabilities) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 429.0	$ 380.2	$ 391.9	$ 330.3
Debt Securities, Available-for-sale, Restricted		67.1	66.1
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		0.1	0.7
Debt Securities, Available-for-sale, Restricted		67.1	66.1
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		48.8	48.5
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[1]	$ 2.5	$ 2.3

[1] The claims reserve represents our liability for incurred-but-not-reported claims and is estimated based on historical claims experience.