Claim and Claim Adjustment Expense Reserves (Net prior year claim and claim adjustment expense reserve development) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Increase (decrease) in provision for insured events of prior years	$ (182)	$ (429)	$ (544)
Property and casualty reserve development [Member]
Increase (decrease) in provision for insured events of prior years	(180)	(429)	(545)
Life reserve development in life company [Member]
Increase (decrease) in provision for insured events of prior years	$ (2)		$ 1