Reinsurance (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in allowance for uncollectible reinsurance receivables	$ (15,000,000)
Funds held under reinsurance agreements, liability	3,600,000,000	4,000,000,000
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations	1,285,000,000	1,121,000,000	1,297,000,000
Ceded claim and claim adjustment expense reserves, future policy benefits and policyholder funds as the result of business operations sold in prior years	1,211,000,000	1,301,000,000
Subsidiaries of Berkshire Hathaway Group [Member]
Ceded Credit Risk, Claims Receivable	2,500,000,000
Subsidiaries of Swiss Re Group [Member]
Ceded Credit Risk, Claims Receivable	1,000,000,000
Subsidiaries of Hartford Insurance Group [Member]
Ceded Credit Risk, Claims Receivable	400,000,000
Significant Captive Program [Member]
Direct and ceded earned premiums	1,500,000,000	1,383,000,000	1,385,000,000
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations	$ 790,000,000	$ 735,000,000	$ 897,000,000