Investments (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	$ (239)	$ (563)	$ (937)
Portion of loss recognized in other comprehensive income	6	(33)	(64)
Net other-than-temporary impairment losses recognized in earnings	(233)	(596)	(1,001)
Fixed income securities
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(150)	(361)	(760)
Portion of loss recognized in other comprehensive income	6	(33)	(64)
Net other-than-temporary impairment losses recognized in earnings	(144)	(394)	(824)
Municipal
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(42)	(59)	(203)
Portion of loss recognized in other comprehensive income	9	(3)	24
Net other-than-temporary impairment losses recognized in earnings	(33)	(62)	(179)
Corporate
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(21)	(30)	(68)
Portion of loss recognized in other comprehensive income	(2)	6	2
Net other-than-temporary impairment losses recognized in earnings	(23)	(24)	(66)
Foreign government
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses		(1)
Net other-than-temporary impairment losses recognized in earnings		(1)
Asset-backed securities ("ABS")
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses		(9)	(14)
Portion of loss recognized in other comprehensive income		2	(16)
Net other-than-temporary impairment losses recognized in earnings		(7)	(30)
Residential mortgage-backed securities ("RMBS")
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(65)	(196)	(381)
Portion of loss recognized in other comprehensive income	(4)	(39)	(47)
Net other-than-temporary impairment losses recognized in earnings	(69)	(235)	(428)
Commercial mortgage-backed securities ("CMBS")
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(22)	(66)	(94)
Portion of loss recognized in other comprehensive income	3	1	(27)
Net other-than-temporary impairment losses recognized in earnings	(19)	(65)	(121)
Equity securities
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(75)	(139)	(57)
Net other-than-temporary impairment losses recognized in earnings	(75)	(139)	(57)
Mortgage loans
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	5	(37)	(71)
Net other-than-temporary impairment losses recognized in earnings	5	(37)	(71)
Limited partnership interests
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(8)	(6)	(46)
Net other-than-temporary impairment losses recognized in earnings	(8)	(6)	(46)
Other
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(11)	(20)	(3)
Net other-than-temporary impairment losses recognized in earnings	$ (11)	$ (20)	$ (3)