Reinsurance (Schedule of Trust Assets and Reinsurance Liabilities) (Details) - USD ($) $ in Millions		Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Reinsurance [Line Items]
Restricted cash and cash equivalents		$ 408.8	$ 410.0	$ 426.7	$ 410.9
Debt Securities, Available-for-sale, Restricted		81.4	72.3
Trust Assets [Member]
Reinsurance [Line Items]
Restricted cash and cash equivalents		1.0	0.4
Debt Securities, Available-for-sale, Restricted		81.4	72.3
Unearned Premium [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities		66.1	54.4
Claims Reserve [Member]
Reinsurance [Line Items]
Accounts payable and accrued liabilities	[1]	$ 6.3	$ 3.1

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