Third-Party Reinsurance - Reinsurance Recoverables (Details) - P&C Insurance and Reinsurance (Ark/WM Outrigger) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Reinsurance recoverables on unpaid losses	$ 507.2	$ 340.8
Reinsurance recoverables on paid losses	27.9	27.4
Ceded unearned premiums	212.9	73.8
Reinsurance recoverables	748.0	442.0
Ark
Segment Reporting Information [Line Items]
Reinsurance recoverables on unpaid losses	(28.0)	(15.6)
Ceded unearned premiums	$ (25.0)	$ (5.7)

The unexpired portion of premiums ceded on policies in force as of the balance sheet date.

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Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer.

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Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

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Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to and paid by the ceding insurer.

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Reinsurance Recoverables on Unpaid Losses, Ceded Unearned Premiums

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