Investments (Net investment income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Net Investment Income
Gross investment income	$ 485		$ 532		$ 1,147		$ 1,167
Investment expense	(15)		(15)		(29)		(30)
Net investment income	470		517		1,118		1,137
Fixed maturity securities [Member]
Net Investment Income
Gross investment income	505		505		1,021		1,011
Short term investments [Member]
Net Investment Income
Gross investment income	2		2		3		4
Limited partnership investments [Member]
Net Investment Income
Gross investment income	(35)		11		95		125
Equity securities [Member]
Net Investment Income
Gross investment income	2		6		6		12
Mortgage loans [Member]
Net Investment Income
Gross investment income	5		2		8		4
Trading portfolio [Member]
Net Investment Income
Gross investment income	4	[1]	3	[1]	11	[1]	6	[1]
Other [Member]
Net Investment Income
Gross investment income	$ 2		$ 3		$ 3		$ 5

[1] There were no net unrealized gains (losses) related to changes in fair value of trading securities still held included in net investment income for the three or six months ended June 30, 2012 or 2011.