Investments (Net investment income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Gross investment income	$ 645	$ 662
Investment expense	(12)	(14)
Net investment income	633	648
Fixed maturity securities [Member]
Gross investment income	499	516
Short term investments [Member]
Gross investment income	1	1
Limited partnership investments [Member]
Gross investment income	131	130
Equity securities [Member]
Gross investment income	3	4
Mortgage loans [Member]
Gross investment income	5	3
Trading portfolio [Member]
Gross investment income	5	7
Other [Member]
Gross investment income	$ 1	$ 1