Investments (Net realized investment gains (losses)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Gain (Loss) on Investments
Net realized investment gains (losses), net of participating policyholders’ interests	$ (4)		$ 86		$ (857)
Fixed maturity securities [Member]
Gain (Loss) on Investments
Gross realized gains	289		475		500
Gross realized losses	(311)		(383)		(1,667)
Net realized investment gains (losses), net of participating policyholders’ interests	(22)		92		(1,167)
Equity securities [Member]
Gain (Loss) on Investments
Gross realized gains	10		50		473
Gross realized losses	(11)		(52)		(230)
Net realized investment gains (losses), net of participating policyholders’ interests	(1)		(2)		243
Derivatives [Member]
Gain (Loss) on Investments
Net realized investment gains (losses), net of participating policyholders’ interests			(1)		51
Short term investments and other [Member]
Gain (Loss) on Investments
Net realized investment gains (losses), net of participating policyholders’ interests	$ 19	[1]	$ (3)	[1]	$ 16	[1]

[1] Includes net unrealized gains (losses) related to changes in the fair value of securities for which the fair value option has been elected. Net unrealized gains (losses) were $2 million and $(1) million for the years ended December 31, 2011 and 2010.