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
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Liability for Claims and Claims Adjustment Expense [Line Items]    
Gross liabilities at the beginning of the year $ 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 14,452 14,638
Losses and loss adjustment expenses incurred, prior accident years (499) (163)
Total Losses and loss adjustment expenses incurred 13,953 14,475
Losses and loss adjustment expenses paid, current accident year (3,673) (3,788)
Losses and loss adjustment expenses paid, prior accident years (9,271) (9,105)
Total Losses and loss adjustment expenses paid (12,944) (12,893)
Foreign currency effect 11 198
Net liabilities at end of year 117,277 112,338
Reinsurance recoverable on unpaid losses at end of year 4,284 4,785
Gross liabilities at end of year $ 121,561 $ 117,123