Reinsurance (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Insurance losses and loss expenses:
Insurance losses and loss expenses, net	$ 3,480	$ 3,444	$ 2,900
Premiums earned, net	4,493	4,214	3,987
Property and casualty insurance
Premiums written:
Direct	4,631	4,271	4,035
Assumed	21	21	19
Ceded	(49)	(37)	(35)
Premiums written, net	4,603	4,255	4,019
Premiums earned:
Direct	4,449	4,164	3,939
Assumed	21	21	20
Ceded	(48)	(36)	(34)
Premiums earned, net	4,422	4,149	3,925
Insurance losses and loss expenses:
Direct	3,382	3,311	2,834
Assumed	10	11	(15)
Ceded	(13)	22	(9)
Insurance losses and loss expenses, net	3,379	3,344	2,810
Life insurance
Premiums earned:
Direct	113	108	104
Ceded	(42)	(43)	(42)
Premiums earned, net	71	65	62
Insurance losses and loss expenses:
Direct	120	120	102
Ceded	(19)	(20)	(12)
Insurance losses and loss expenses, net	$ 101	$ 100	$ 90