Insurance Claim Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
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	$ 58,649
Net reserves at end of year	53,804
Reinsurance recoverables on unpaid losses	7,823
Claims and claim adjustment expense reserves at end of year	61,627	$ 58,649
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	58,643	56,897	$ 54,510
Reinsurance recoverables on unpaid losses	7,790	8,209	8,153
Net reserves at beginning of year	50,853	48,688	46,357
Estimated claims and claim adjustment expenses for claims arising in the current year	26,159	23,308	20,698
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(38)	(537)	(484)
Total increases	26,121	22,771	20,214
Claims and claim adjustment expense payments for claims arising in current year	10,852	9,406	8,401
Claims and claim adjustment expense payments for claims arising in prior years	12,424	10,945	9,470
Total payments	23,276	20,351	17,871
Unrealized foreign exchange loss (gain)	106	(255)	(12)
Net reserves at end of year	53,804	50,853	48,688
Reinsurance recoverables on unpaid losses	7,817	7,790	8,209
Claims and claim adjustment expense reserves at end of year	61,621	58,643	56,897
Amount of increase in gross claims and claim adjustment expense reserves	2,980	1,750
Amount of increase (decrease) in reinsurance recoverables on unpaid losses	27	(419)
Reserves for long-term disability and annuity claim payments primarily arising from workers' compensation insurance and workers' compensation excess insurance policies, net of discount	2,680	2,720
Discount included in reserves for long-term disability and annuity claim payments primarily arising from workers' compensation insurance and workers' compensation excess insurance policies	1,100	1,120
Accretion expense	$ 45	$ 46	$ 48
Property-casualty [Member] | Minimum [Member]
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]
Reserves for long-term disability and annuity claim payments primarily arising from workers' compensation insurance and workers' compensation excess insurance policies, discount rate (percent)	3.50%	3.50%
Property-casualty [Member] | Maximum [Member]
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]
Reserves for long-term disability and annuity claim payments primarily arising from workers' compensation insurance and workers' compensation excess insurance policies, discount rate (percent)	5.00%	5.00%
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
Net reserves at end of year	0
Reinsurance recoverables on unpaid losses	6
Claims and claim adjustment expense reserves at end of year	$ 6	$ 6