Segments Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues [Abstract]
Premiums earned related to reinsurance assumed									$ 13	$ 13	$ 48
Premiums earned related to insurance business									11,631	11,202	11,283
Net premiums earned									11,644	11,215	11,331
Investment Income									1,644	1,665	1,649
Corporate and other revenues									55	88	75
Realized investment gains, Net									288	426	23
Revenues	3,345	3,420	3,400	3,420	3,411	3,267	3,318	3,323	13,585	13,319	13,016
Property and casualty insurance [Member]
Revenues [Abstract]
Investment Income									1,598	1,590	1,585
Other revenues									0	0	2
Revenues									13,242	12,805	12,918
Personal insurance [Member]
Revenues [Abstract]
Premiums earned related to insurance business									3,917	3,768	3,692
Commercial insurance [Member]
Revenues [Abstract]
Premiums earned related to insurance business									4,945	4,647	4,762
Specialty insurance [Member]
Revenues [Abstract]
Premiums earned related to insurance business									$ 2,769	$ 2,787	$ 2,829