Investments (Net realized investment gains (losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net realized investment gains (losses), net of participating policyholders’ interests	$ 8	$ (27)	$ 66	$ 1
Fixed maturity securities [Member]
Available-for-sale Securities, Gross Realized Gains	75	56	193	233
Available-for-sale Securities, Gross Realized Losses	(49)	(85)	(120)	(222)
Net realized investment gains (losses), net of participating policyholders’ interests	26	(29)	73	11
Equity securities [Member]
Available-for-sale Securities, Gross Realized Gains	5	1	10	7
Available-for-sale Securities, Gross Realized Losses	(20)	(2)	(24)	(10)
Net realized investment gains (losses), net of participating policyholders’ interests	(15)	(1)	(14)	(3)
Gain (Loss) on Derivatives [Member]
Net realized investment gains (losses), net of participating policyholders’ interests	(1)	1	(1)
Short term and other [Member]
Net realized investment gains (losses), net of participating policyholders’ interests	$ (2)	$ 2	$ 8	$ (7)