Insurance Claim Reserves (Details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
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	$ 61,627
Claims and claim adjustment expense reserves at end of period	64,746
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	61,621	$ 58,643
Reinsurance recoverables on unpaid losses	7,817	7,790
Net reserves at beginning of year	53,804	50,853
Estimated claims and claim adjustment expenses for claims arising in the current year	21,276	20,205
Estimated increase (decrease) in claims and claim adjustment expenses for claims arising in prior years	(321)	62
Total increases	20,955	20,267
Claims and claim adjustment expense payments for claims arising in current year	7,255	7,305
Claims and claim adjustment expense payments for claims arising in prior years	10,545	10,031
Total payments	17,800	17,336
Unrealized foreign exchange (gain) loss	38	(1)
Net reserves at end of period	56,997	53,783
Reinsurance recoverables on unpaid losses	7,744	7,920
Claims and claim adjustment expense reserves at end of period	64,741	$ 61,703
Amount of increase in gross claims and claim adjustment expense reserves	3,120
Amount of decrease in reinsurance recoverables on unpaid losses	(73)
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	6
Claims and claim adjustment expense reserves at end of period	$ 5