Insurance Claim Reserves (Details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
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	$ 51,849
Reinsurance recoverables, allowance for estimated uncollectible reinsurance	149		$ 92
Claims and claim adjustment expense reserves at end of period	51,957
Accounting Standards Update 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]
Reinsurance recoverables, allowance for estimated uncollectible reinsurance			53
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	51,836	$ 50,653
Reinsurance recoverables on unpaid losses	8,035	8,182
Net reserves at beginning of year	43,854	42,471
Estimated claims and claim adjustment expenses for claims arising in the current year	4,763	4,435
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(3)	(16)
Total increases	4,760	4,419
Claims and claim adjustment expense payments for claims arising in current year	947	970
Claims and claim adjustment expense payments for claims arising in prior years	3,439	3,320
Total payments	4,386	4,290
Unrealized foreign exchange (gain) loss	(210)	41
Net reserves at end of period	44,018	42,641
Reinsurance recoverables on unpaid losses	7,926	8,063
Claims and claim adjustment expense reserves at end of period	51,944	$ 50,704
Amount of increase in gross claims and claim adjustment expense reserves	108
Amount of decrease in reinsurance recoverables on unpaid losses	109
Property-casualty [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Reconciliation of beginning and ending reserve balances for claims and claim adjustment expenses [Roll Forward]
Reinsurance recoverables, allowance for estimated uncollectible reinsurance			$ 53
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	13
Claims and claim adjustment expense reserves at end of period	$ 13