Investments (Net investment income) (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
Gross investment income	$ 614	$ 409	$ 1,761	$ 1,576
Investment expense	(13)	(15)	(42)	(45)
Net investment income	601	394	1,719	1,531
Fixed maturity securities [Member]
Gross investment income	507	494	1,528	1,505
Short term investments [Member]
Gross investment income	2	2	5	6
Limited partnership investments [Member]
Gross investment income	89	(93)	184	32
Equity securities [Member]
Gross investment income	4	4	10	16
Mortgage loans [Member]
Gross investment income	5	2	13	6
Trading portfolio [Member]
Gross investment income	7	(1)	18	5
Other [Member]
Gross investment income		$ 1	$ 3	$ 6