Investments (Net investment income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Gross investment income	$ 611	$ 614	$ 1,848	$ 1,761
Investment expense	(14)	(13)	(40)	(42)
Net investment income	597	601	1,808	1,719
Fixed maturity securities [Member]
Gross investment income	504	507	1,501	1,528
Short term investments [Member]
Gross investment income	1	2	3	5
Limited partnership investments [Member]
Gross investment income	93	89	303	184
Equity securities [Member]
Gross investment income	3	4	9	10
Mortgage loans [Member]
Gross investment income	6	5	17	13
Trading portfolio [Member]
Gross investment income	3	7	13	18
Other [Member]
Gross investment income	$ 1		$ 2	$ 3