Insurance Claim Reserves (Details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
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	$ 50,668
Claims and claim adjustment expense reserves at end of period	51,073
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	50,653	$ 49,633
Reinsurance recoverables on unpaid losses	8,182	8,123
Net reserves at beginning of year	42,471	41,510
Estimated claims and claim adjustment expenses for claims arising in the current year	9,329	9,084
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(118)	(268)
Total increases	9,211	8,816
Claims and claim adjustment expense payments for claims arising in current year	2,810	2,851
Claims and claim adjustment expense payments for claims arising in prior years	5,897	5,454
Total payments	8,707	8,305
Unrealized foreign exchange (gain) loss	62	(102)
Net reserves at end of period	43,037	41,919
Reinsurance recoverables on unpaid losses	8,022	8,026
Claims and claim adjustment expense reserves at end of period	51,059	$ 49,945
Amount of increase in gross claims and claim adjustment expense reserves	406
Amount of decrease in reinsurance recoverables on unpaid losses	(160)
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	15
Claims and claim adjustment expense reserves at end of period	$ 14