Investments (Details 10) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 security	Dec. 31, 2012 security
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	219	160
Fair value, continuous unrealized loss position for less than 12 months	$ 2,146	$ 1,513
Unrealized losses, continuous unrealized loss position for less than 12 months	(40)	(36)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	354	401
Fair value, continuous unrealized loss position for 12 months or more	2,339	2,787
Unrealized losses, continuous unrealized loss position for 12 months or more	(282)	(391)
Total unrealized losses
Total unrealized losses	(322)	(427)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	215	157
Fair value, continuous unrealized loss position for less than 12 months	2,118	1,456
Unrealized losses, continuous unrealized loss position for less than 12 months	(39)	(35)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	354	400
Fair value, continuous unrealized loss position for 12 months or more	2,339	2,787
Unrealized losses, continuous unrealized loss position for 12 months or more	(282)	(391)
Total unrealized losses
Gross unrealized losses	(321)	(426)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	2	1
Fair value, continuous unrealized loss position for less than 12 months	18	15
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	6	11
Fair value, continuous unrealized loss position for less than 12 months	66	101
Unrealized losses, continuous unrealized loss position for less than 12 months	(4)	(7)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	29	50
Fair value, continuous unrealized loss position for 12 months or more	167	395
Unrealized losses, continuous unrealized loss position for 12 months or more	(25)	(54)
Total unrealized losses
Total unrealized losses	(29)	(61)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	149	79
Fair value, continuous unrealized loss position for less than 12 months	1,830	1,086
Unrealized losses, continuous unrealized loss position for less than 12 months	(32)	(27)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	63	66
Fair value, continuous unrealized loss position for 12 months or more	792	829
Unrealized losses, continuous unrealized loss position for 12 months or more	(83)	(86)
Total unrealized losses
Total unrealized losses	(115)	(113)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	2	2
Fair value, continuous unrealized loss position for less than 12 months	120	121
Unrealized losses, continuous unrealized loss position for less than 12 months	(2)	(1)
Total unrealized losses
Total unrealized losses	(2)	(1)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	2	5
Fair value, continuous unrealized loss position for less than 12 months	11	38
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	75	76
Fair value, continuous unrealized loss position for 12 months or more	772	763
Unrealized losses, continuous unrealized loss position for 12 months or more	(85)	(105)
Total unrealized losses
Total unrealized losses	(85)	(105)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	48	49
Fair value, continuous unrealized loss position for less than 12 months	16	30
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	160	164
Fair value, continuous unrealized loss position for 12 months or more	378	442
Unrealized losses, continuous unrealized loss position for 12 months or more	(48)	(69)
Total unrealized losses
Total unrealized losses	(48)	(69)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	6	10
Fair value, continuous unrealized loss position for less than 12 months	57	65
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	27	43
Fair value, continuous unrealized loss position for 12 months or more	230	358
Unrealized losses, continuous unrealized loss position for 12 months or more	(41)	(77)
Total unrealized losses
Total unrealized losses	(42)	(77)
Redeemable preferred stock
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more		1
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	156	132
Fair value, continuous unrealized loss position for less than 12 months	1,815	1,244
Unrealized losses, continuous unrealized loss position for less than 12 months	(32)	(29)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	237	262
Fair value, continuous unrealized loss position for 12 months or more	1,574	1,919
Unrealized losses, continuous unrealized loss position for 12 months or more	(148)	(195)
Total unrealized losses
Total unrealized losses	(180)	(224)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	59	25
Fair value, continuous unrealized loss position for less than 12 months	303	212
Unrealized losses, continuous unrealized loss position for less than 12 months	(7)	(6)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	117	138
Fair value, continuous unrealized loss position for 12 months or more	765	868
Unrealized losses, continuous unrealized loss position for 12 months or more	(134)	(196)
Total unrealized losses
Total unrealized losses	(141)	(202)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	4	3
Fair value, continuous unrealized loss position for less than 12 months	28	57
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more		1
Total unrealized losses
Gross unrealized losses on equity securities	$ (1)	$ (1)