Investments (Details 6) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	$ (27)	$ (87)
Portion of loss recognized in other comprehensive income	(10)	4
Net other-than-temporary impairment losses recognized in earnings	(37)	(83)
Fixed income securities
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(32)	(68)
Portion of loss recognized in other comprehensive income	(10)	4
Net other-than-temporary impairment losses recognized in earnings	(42)	(64)
Municipal
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(13)	(1)
Portion of loss recognized in other comprehensive income	(2)
Net other-than-temporary impairment losses recognized in earnings	(15)	(1)
Corporate
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses		(18)
Net other-than-temporary impairment losses recognized in earnings		(18)
Residential mortgage-backed securities ("RMBS")
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses		(43)
Portion of loss recognized in other comprehensive income	(1)	4
Net other-than-temporary impairment losses recognized in earnings	(1)	(39)
Commercial mortgage-backed securities ("CMBS")
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(19)	(6)
Portion of loss recognized in other comprehensive income	(7)
Net other-than-temporary impairment losses recognized in earnings	(26)	(6)
Equity securities
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(19)	(16)
Net other-than-temporary impairment losses recognized in earnings	(19)	(16)
Mortgage loans
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	26	(3)
Net other-than-temporary impairment losses recognized in earnings	26	(3)
Limited partnership interests
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses		(2)
Net other-than-temporary impairment losses recognized in earnings		(2)
Other
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment losses	(2)	2
Net other-than-temporary impairment losses recognized in earnings	$ (2)	$ 2