Insurance Claim Reserves (Details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 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	62,487
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	6,679	6,025
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(49)	(90)
Total increases	6,630	5,935
Claims and claim adjustment expense payments for claims arising in current year	1,275	1,177
Claims and claim adjustment expense payments for claims arising in prior years	4,435	4,382
Total payments	5,710	5,559
Unrealized foreign exchange (gain) loss	(61)	28
Net reserves at end of period	54,663	51,257
Reinsurance recoverables on unpaid losses	7,819	7,801
Claims and claim adjustment expense reserves at end of period	62,482	$ 59,058
Amount of increase in gross claims and claim adjustment expense reserves	861
Amount of increase in reinsurance recoverables on unpaid losses	2
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