Reinsurance (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property-liability insurance premiums written
Direct	$ 28,103	$ 27,066	$ 26,984
Assumed	35	22	29
Ceded	(1,111)	(1,108)	(1,106)
Property-liability insurance premiums written, net of reinsurance	27,027	25,980	25,907
Property-liability insurance premiums earned
Direct	27,794	27,016	27,015
Assumed	33	24	34
Ceded	(1,090)	(1,098)	(1,092)
Property-liability insurance premiums earned, net of reinsurance	26,737	25,942	25,957
Life and annuity premiums and contract charges
Direct	2,860	2,953	2,935
Assumed	55	35	37
Ceded	(674)	(750)	(804)
Life and annuity premiums and contract charges, net of reinsurance	$ 2,241	$ 2,238	$ 2,168