Insurance Claim Reserves (details) - Reserve Detail for Claims and Claim Adjustment Expenses - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 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	48,574
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	8,493	7,859
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years	(214)	(418)
Total increases	8,279	7,441
Claims and claim adjustment expense payments for claims arising in current year	2,699	2,454
Claims and claim adjustment expense payments for claims arising in prior years	4,966	5,004
Total payments	7,665	7,458
Unrealized foreign exchange loss	117	36
Net reserves at end of period	40,679	39,842
Reinsurance recoverables on unpaid losses	7,877	8,089
Claims and claim adjustment expense reserves at end of period	48,556	$ 47,931
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	$ 18