Reinsurance (Schedule of Trust Assets and Reinsurance Liabilities) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 481.1	$ 410.9	$ 538.5	$ 380.2
Debt Securities, Available-for-sale, Restricted		62.4	62.1
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		1.1	0.3
Debt Securities, Available-for-sale, Restricted		62.4	62.1
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		48.5	44.6
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[1]	$ 2.3	$ 2.4

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