Insurance Claim Reserves (Details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 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	51,612
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	14,193	13,707
Estimated increase (decrease) in claims and claim adjustment expenses for claims arising in prior years	214	(255)
Total increases	14,407	13,452
Claims and claim adjustment expense payments for claims arising in current year	5,174	5,112
Claims and claim adjustment expense payments for claims arising in prior years	8,034	7,419
Total payments	13,208	12,531
Unrealized foreign exchange (gain) loss	12	(82)
Net reserves at end of period	43,682	42,349
Reinsurance recoverables on unpaid losses	7,916	8,066
Claims and claim adjustment expense reserves at end of period	51,598	$ 50,415
Amount of increase in gross claims and claim adjustment expense reserves	945
Amount of decrease in reinsurance recoverables on unpaid losses	266
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