Investments (Net investment income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Gross investment income	$ 592	$ 485	$ 1,237	$ 1,147
Investment expense	(14)	(15)	(26)	(29)
Net investment income	578	470	1,211	1,118
Fixed maturity securities [Member]
Gross investment income	498	505	997	1,021
Short term investments [Member]
Gross investment income	1	2	2	3
Limited partnership investments [Member]
Gross investment income	79	(35)	210	95
Equity securities [Member]
Gross investment income	3	2	6	6
Mortgage loans [Member]
Gross investment income	6	5	11	8
Trading portfolio [Member]
Gross investment income	5	4	10	11
Other [Member]
Gross investment income		$ 2	$ 1	$ 3