v3.26.1
Unpaid losses and loss adjustment expenses - Reconciliation of changes in claim liabilities (Detail) - Property and Casualty Insurance and Reinsurance, Excluding Retroactive Reinsurance [Member] - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Liability for Claims and Claims Adjustment Expense [Line Items]    
Gross liabilities at the beginning of the period $ 120,713 $ 115,151
Reinsurance recoverable on unpaid losses at the beginning of the year (4,456) (4,593)
Net liabilities at the beginning of the year 116,257 110,558
Losses and loss adjustment expenses incurred, current accident year 29,517 28,607
Losses and loss adjustment expenses incurred, prior accident years (1,467) (240)
Total Losses and loss adjustment expenses incurred 28,050 28,367
Losses and loss adjustment expenses paid, current accident year (9,571) (9,253)
Losses and loss adjustment expenses paid, prior accident years (16,121) (16,283)
Total Losses and loss adjustment expenses paid (25,692) (25,536)
Foreign currency effect 25 712
Net liabilities at end of period 118,640 114,101
Reinsurance recoverable on unpaid losses at end of period 4,235 4,687
Gross liabilities at end of period $ 122,875 $ 118,788