For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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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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Third-Party Reinsurance - Remaining Gross and Net Reinsurance Recoverables (Details) - P&C Insurance and Reinsurance (Ark/WM Outrigger) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Segment Reporting Information [Line Items]
Gross	$ 538.0
Collateral	1,044.1	$ 589.0
Net	$ 451.9
Reinsurer Concentration Risk \| Reinsurance Recoverable Including Reinsurance Premium Paid
Segment Reporting Information [Line Items]
% of Total	100.00%
Ceded Credit Risk, Secured
Segment Reporting Information [Line Items]
Collateral	$ 86.1
A+ or better
Segment Reporting Information [Line Items]
Gross	319.1
Net	$ 319.1
A+ or better \| Reinsurer Concentration Risk \| Reinsurance Recoverable Including Reinsurance Premium Paid
Segment Reporting Information [Line Items]
% of Total	70.60%
A+ or better \| Ceded Credit Risk, Secured
Segment Reporting Information [Line Items]
Collateral	$ 0.0
A- to A
Segment Reporting Information [Line Items]
Gross	113.0
Net	$ 113.0
A- to A \| Reinsurer Concentration Risk \| Reinsurance Recoverable Including Reinsurance Premium Paid
Segment Reporting Information [Line Items]
% of Total	25.00%
A- to A \| Ceded Credit Risk, Secured
Segment Reporting Information [Line Items]
Collateral	$ 0.0
B++ or lower and not rated (2)
Segment Reporting Information [Line Items]
Gross	105.9
Net	19.8
B++ or lower and not rated (2) \| Ark
Segment Reporting Information [Line Items]
Gross	(40.3)
Collateral	$ (40.3)
B++ or lower and not rated (2) \| Reinsurer Concentration Risk \| Reinsurance Recoverable Including Reinsurance Premium Paid
Segment Reporting Information [Line Items]
% of Total	4.40%
B++ or lower and not rated (2) \| Ceded Credit Risk, Secured
Segment Reporting Information [Line Items]
Collateral	$ 86.1