Insurance Claim Reserves (details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
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	$ 47,949
Claims and claim adjustment expense reserves at end of period	49,750
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	47,929	$ 48,272
Reinsurance recoverables on unpaid losses	7,981	8,449
Net reserves at beginning of year	39,948	39,823
Estimated claims and claim adjustment expenses for claims arising in the current year	13,261	11,708
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(197)	(430)
Total increases	13,064	11,278
Claims and claim adjustment expense payments for claims arising in current year	4,799	4,334
Claims and claim adjustment expense payments for claims arising in prior years	6,831	6,778
Total payments	11,630	11,112
Unrealized foreign exchange loss	215	12
Net reserves at end of period	41,597	40,001
Reinsurance recoverables on unpaid losses	8,136	8,146
Claims and claim adjustment expense reserves at end of period	49,733	$ 48,147
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	20
Claims and claim adjustment expense reserves at end of period	$ 17