Related Party Transactions - Schedule of Commissions (Details) - Related Party - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Related Party Transaction [Line Items]
Ceding commission expense	$ 78.4	$ 70.6	$ 155.0	$ 149.0
Profit commission expense	(7.9)	0.0	2.3	0.0
Total commissions	$ 70.5	$ 70.6	$ 157.3	$ 149.0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details