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Reinsurance and Indemnification - Canada Catastrophe Excess of Loss Reinsurance Contract (Narrative) (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) reinstatement	Dec. 31, 2025 CAD ($) reinstatement	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 2,681		$ 2,260	$ 2,036
Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 1,230		$ 1,110	$ 1,020
Canada Catastrophe Excess of Loss | Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Limit of aggregate losses under aggregate excess agreement		$ 478
Retention amount for catastrophe reinsurance agreement contracts		$ 100
Number of reinstatements each year for each contract | reinstatement	1	1

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The limit of aggregated losses per contract year beyond which coverage provided by an aggregate excess agreement applies.

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