Reinsurance (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reduction in allowance for doubtful accounts	$ 15,000,000
Reinsurance collateral	3,600,000,000	4,000,000,000
Reinsurance recoveries	1,300,000,000	1,100,000,000	1,300,000,000
Ceded claim and claim adjustment expense reserves, future policy benefits and policyholders' funds as a result of business operations sold in prior years	1,200,000,000	1,300,000,000
Subsidiaries From Swiss Re Group [Member]
Largest recoverables from a single reinsurer	1,000,000,000
Berkshire Hathaway Group [Member]
Largest recoverables from a single reinsurer	2,500,000,000
Subsidiaries From Hartford Insurance Group [Member]
Largest recoverables from a single reinsurer	400,000,000
Significant Captive Program [Member]
Direct and ceded earned premiums	1,500,000,000	1,400,000,000	1,400,000,000
Percentage reinsured of direct and ceded earned premiums	100.00%
Reinsurance recoveries	$ 790,000,000	$ 735,000,000	$ 897,000,000