Supplemental Information Concerning Property-Casualty Insurance Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Deferred policy acquisition costs	$ 204		$ 189
Reserves for unpaid claims and claim adjustment expenses	6,845	[1]	6,520	[1]
Discount deducted from reserves	22	[2]	30	[2]
Unearned premiums	1,651	[3]	1,484	[3]
Earned premiums	2,847		2,759		2,550
Net investment income	256		271		320
Claims and claim adjustment expenses incurred related to current year	1,903		1,813		1,615
Claims and claim adjustment expenses incurred related to prior years	(30)		(69)		(158)
Amortization of deferred policy acquisition costs	423		425		404
Paid claims and claim adjustment expenses	2,026		1,621		1,476
Premiums written	$ 2,949		$ 2,770		$ 2,408

[1] Grossed up for reinsurance recoverables of $2,716 and $2,238 at December 31, 2012 and 2011, respectively.

[2] Discounted at approximately 4.5% and 6% at December 31, 2012 and 2011, respectively.

[3] Grossed up for prepaid reinsurance premiums of $471 and $409 at December 31, 2012 and 2011, respectively.