Insurance Claim Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
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
Net reserves at end of year	56,419
Reinsurance recoverables on unpaid losses	7,674
Claims and claim adjustment expense reserves at end of year	64,093	$ 61,627
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	$ 56,897
Reinsurance recoverables on unpaid losses	7,817	7,790	8,209
Net reserves at beginning of year	53,804	50,853	48,688
Estimated claims and claim adjustment expenses for claims arising in the current year	27,508	26,159	23,308
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(548)	(38)	(537)
Total increases	26,960	26,121	22,771
Claims and claim adjustment expense payments for claims arising in current year	10,924	10,852	9,406
Claims and claim adjustment expense payments for claims arising in prior years	13,227	12,424	10,945
Total payments	24,151	23,276	20,351
Unrealized foreign exchange (gain) loss	(194)	106	(255)
Net reserves at end of year	56,419	53,804	50,853
Reinsurance recoverables on unpaid losses	7,669	7,817	7,790
Claims and claim adjustment expense reserves at end of year	64,088	61,621	58,643
Amount of increase in gross claims and claim adjustment expense reserves	2,470	2,980
Amount of increase (decrease) in reinsurance recoverables on unpaid losses	(148)	27
Reserves for long-term disability and annuity claim payments primarily arising from workers' compensation insurance and workers' compensation excess insurance policies, net of discount	2,650	2,680
Discount included in reserves for long-term disability and annuity claim payments primarily arising from workers' compensation insurance and workers' compensation excess insurance policies	1,070	1,100
Accretion expense	$ 44	$ 45	$ 46
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	5
Claims and claim adjustment expense reserves at end of year	$ 5	$ 6