Reinsurance (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Premiums earned:
Direct	$ 4,272	$ 4,043	$ 3,906
Assumed	21	20	42
Ceded	(79)	(76)	(79)
Premiums earned, net	4,214	3,987	3,869
Insurance losses and loss expenses:
Insurance losses and loss expense, net	3,444	2,900	2,728
Property and casualty insurance
Premiums written:
Direct	4,271	4,035	3,861
Assumed	21	19	30
Ceded	(37)	(35)	(30)
Premiums written, net	4,255	4,019	3,861
Premiums earned:
Direct	4,164	3,939	3,806
Assumed	21	20	42
Ceded	(36)	(34)	(40)
Premiums earned, net	4,149	3,925	3,808
Insurance losses and loss expenses:
Direct	3,311	2,834	2,655
Assumed	11	(15)	12
Ceded	22	(9)	(28)
Insurance losses and loss expense, net	3,344	2,810	2,639
Life insurance
Premiums earned:
Direct	108	104	100
Ceded	(43)	(42)	(39)
Premiums earned, net	65	62	61
Insurance losses and loss expenses:
Direct	120	102	114
Ceded	(20)	(12)	(25)
Insurance losses and loss expense, net	$ 100	$ 90	$ 89