Other Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Ceding commission receivable	$ 19.4	$ 21.0
Right-of-use assets (Note 22)	17.4	26.4
Prepaid expenses	12.0	14.0
Investment income due and accrued	5.5	3.7
Income tax receivable	1.5	5.0
Other	8.0	5.1
Total other assets	$ 63.8	$ 75.2
Operating lease, right-of-use asset, statement of financial position	Total other assets	Total other assets