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Commitments and Contingencies - Concentrations of credit risk (Details)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Customer concentration risk | Gross written premiums
Concentration Risk [Line Items]
Concentration risk, threshold	10.00%
Customer concentration risk | Gross written premiums | Marsh & McLennan Companies and its subsidiaries
Concentration Risk [Line Items]
Concentration risk percentage	16.60%	18.60%	19.00%
Customer concentration risk | Gross written premiums | AON Corporation and its subsidiaries
Concentration Risk [Line Items]
Concentration risk percentage	14.60%	14.50%	13.90%
Credit concentration risk | Shareholders' equity
Concentration Risk [Line Items]
Concentration risk, threshold	10.00%

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