Investments (Net realized investment gains (losses)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net realized investment gains (losses), net of participating policyholders’ interests	$ 63	$ (2)	$ 86
Fixed maturity securities [Member]
Gross realized gains	232	289	475
Gross realized losses	(149)	(311)	(383)
Net realized investment gains (losses), net of participating policyholders’ interests	83	(22)	92
Equity securities [Member]
Gross realized gains	19	10	50
Gross realized losses	(42)	(11)	(52)
Net realized investment gains (losses), net of participating policyholders’ interests	(23)	(1)	(2)
Derivative [Member]
Net realized investment gains (losses), net of participating policyholders’ interests	(2)		(1)
Short term investments and other [Member]
Net realized investment gains (losses), net of participating policyholders’ interests	$ 5	$ 21	$ (3)