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, 2011	Dec. 31, 2010	Dec. 31, 2009
Increase (decrease) in provision for insured events of prior years	$ (429)	$ (544)	$ (240)
Core (Non-A&EP) [Member]
Increase (decrease) in provision for insured events of prior years	(429)	(545)	(396)
A&EP [Member]
Increase (decrease) in provision for insured events of prior years			155
Property and casualty reserve development [Member]
Increase (decrease) in provision for insured events of prior years	(429)	(545)	(241)
Life reserve development in life company [Member]
Increase (decrease) in provision for insured events of prior years		$ 1	$ 1