Insurance Claim Reserves (details) - Reconciliation of Beginning and Ending Property Casualty Reserve Balances for Claims and Claim Adjustment Expenses (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of beginning and ending property casualty reserve balances for claims and claim adjustment expenses [Roll Forward]
Claims and claim adjustment expense reserves at beginning of year, property casualty	$ 51,353	$ 51,537
Estimated claims and claim adjustment expenses for claims arising in the current year, property casualty	15,559	16,937	14,452
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years, property casualty	(1,074)	(842)	(1,417)
Total payments, property casualty reserves	14,833	15,404	13,697
Claims and claim adjustment expense reserves at end of year, property casualty	50,888	51,353	51,537
Property casualty reserves [Member]
Reconciliation of beginning and ending property casualty reserve balances for claims and claim adjustment expenses [Roll Forward]
Claims and claim adjustment expense reserves at beginning of year, property casualty	51,353	51,537	53,529
Reinsurance recoverables on unpaid losses, property casualty	10,434	11,282	12,588
Net reserves at beginning of year, property casualty	40,919	40,255	40,941
Estimated claims and claim adjustment expenses for claims arising in the current year, property casualty	15,559	16,937	14,452
Estimated decrease in claims and claim adjustment expenses for claims arising in prior years, property casualty	(1,074)	(842)	(1,417)
Total increases, property casualty reserves	14,485	16,095	13,035
Claims and claim adjustment expense payments for claims arising in current year, property casualty	6,507	7,751	5,949
Claims and claim adjustment expense payments for claims arising in prior years, property casualty	8,326	7,653	7,748
Total payments, property casualty reserves	14,833	15,404	13,697
Unrealized foreign exchange (gain) loss, property casualty reserves	63	(27)	(24)
Net reserves at end of year, property casualty	40,634	40,919	40,255
Reinsurance recoverables on unpaid losses, property casualty	10,254	10,434	11,282
Claims and claim adjustment expense reserves at end of year, property casualty	$ 50,888	$ 51,353	$ 51,537