Insurance Claim Reserves (details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Insurance Claim Reserves disclosure
Claims and claim adjustment expense reserves, property-casualty	$ 50,888,000,000	$ 51,353,000,000	$ 51,537,000,000
Claims and claim adjustment expense reserves, accident and health	34,000,000	39,000,000
Claims and claim adjustment expense reserves	50,922,000,000	51,392,000,000	51,581,000,000
Amount of decrease in gross claims and claim adjustment expense reserves	465,000,000	184,000,000
Amount of decline in reinsurance recoverables on unpaid losses	180,000,000	848,000,000
Accretion of discount	48,000,000	45,000,000	45,000,000
Net favorable prior year reserve development for accident years 2009 and prior		1,100,000,000
Net unfavorable prior year reserve development for accident year 2010		383,000,000
Asbestos and environmental claims reserves, balance	2,730,000,000	2,780,000,000
Percent of total asbestos net paid losses related to policyholders with whom the Company had entered into settlement agreements limiting the Company's liability	6.00%	19.00%	32.00%
Benefit from the reduction in the allowance for uncollectible reinsurance resulting from a favorable ruling related to a reinsurance dispute			$ 70,000,000