v3.25.3
Insurance Claim Reserves (Details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]    
Claims and claim adjustment expense reserves at beginning of year $ 64,093  
Claims and claim adjustment expense reserves at end of period 67,705  
Property-casualty [Member]    
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]    
Claims and claim adjustment expense reserves at beginning of year 64,088 $ 61,621
Reinsurance recoverables on unpaid losses 7,669 7,817
Net reserves at beginning of year 56,419 53,804
Estimated claims and claim adjustment expenses for claims arising in the current year 21,959 21,276
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years (648) (321)
Total increases 21,311 20,955
Claims and claim adjustment expense payments for claims arising in current year 7,597 7,255
Claims and claim adjustment expense payments for claims arising in prior years 10,623 10,545
Total payments 18,220 17,800
Unrealized foreign exchange loss 204 38
Net reserves at end of period 59,714 56,997
Reinsurance recoverables on unpaid losses 7,987 7,744
Claims and claim adjustment expense reserves at end of period 67,701 $ 64,741
Amount of increase in gross claims and claim adjustment expense reserves 3,610  
Accident and health [Member]    
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]    
Claims and claim adjustment expense reserves at beginning of year 5  
Claims and claim adjustment expense reserves at end of period $ 4