Retroactive reinsurance contracts - Narrative (Detail) - USD ($) $ in Billions	Jun. 30, 2025	Dec. 31, 2024
Retroactive Reinsurance [Member]
Effects of Reinsurance [Line Items]
Deferred charge assets on retroactive reinsurance contracts	$ 8.5	$ 8.8

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.

No definition available.

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