Segment Information - Schedule of Earned Premiums by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 234.3	$ 342.7	$ 837.9	$ 1,062.5
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	210.4	314.2	762.1	951.1
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	0.0	0.0	0.0	48.3
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 23.9	$ 28.5	$ 75.8	$ 63.1