Investments (Details 10) (USD $) In Millions, unless otherwise specified	Jun. 30, 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	742	160
Fair value, continuous unrealized loss position for less than 12 months	$ 7,553	$ 1,513
Unrealized losses, continuous unrealized loss position for less than 12 months	(340)	(36)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	311	401
Fair value, continuous unrealized loss position for 12 months or more	1,919	2,787
Unrealized losses, continuous unrealized loss position for 12 months or more	(241)	(391)
Total unrealized losses
Total unrealized losses	(581)	(427)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	708	157
Fair value, continuous unrealized loss position for less than 12 months	7,444	1,456
Unrealized losses, continuous unrealized loss position for less than 12 months	(333)	(35)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	311	400
Fair value, continuous unrealized loss position for 12 months or more	1,919	2,787
Unrealized losses, continuous unrealized loss position for 12 months or more	(241)	(391)
Total unrealized losses
Gross unrealized losses	(574)	(426)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	4	1
Fair value, continuous unrealized loss position for less than 12 months	57	15
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)
Total unrealized losses
Total unrealized losses	(1)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	49	11
Fair value, continuous unrealized loss position for less than 12 months	365	101
Unrealized losses, continuous unrealized loss position for less than 12 months	(18)	(7)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	28	50
Fair value, continuous unrealized loss position for 12 months or more	143	395
Unrealized losses, continuous unrealized loss position for 12 months or more	(35)	(54)
Total unrealized losses
Total unrealized losses	(53)	(61)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	543	79
Fair value, continuous unrealized loss position for less than 12 months	6,460	1,086
Unrealized losses, continuous unrealized loss position for less than 12 months	(295)	(27)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	54	66
Fair value, continuous unrealized loss position for 12 months or more	677	829
Unrealized losses, continuous unrealized loss position for 12 months or more	(85)	(86)
Total unrealized losses
Total unrealized losses	(380)	(113)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	8	2
Fair value, continuous unrealized loss position for less than 12 months	183	121
Unrealized losses, continuous unrealized loss position for less than 12 months	(10)	(1)
Total unrealized losses
Total unrealized losses	(10)	(1)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	3	5
Fair value, continuous unrealized loss position for less than 12 months	26	38
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	70	76
Fair value, continuous unrealized loss position for 12 months or more	729	763
Unrealized losses, continuous unrealized loss position for 12 months or more	(69)	(105)
Total unrealized losses
Total unrealized losses	(69)	(105)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	80	49
Fair value, continuous unrealized loss position for less than 12 months	131	30
Unrealized losses, continuous unrealized loss position for less than 12 months	(4)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	139	164
Fair value, continuous unrealized loss position for 12 months or more	238	442
Unrealized losses, continuous unrealized loss position for 12 months or more	(25)	(69)
Total unrealized losses
Total unrealized losses	(29)	(69)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	21	10
Fair value, continuous unrealized loss position for less than 12 months	222	65
Unrealized losses, continuous unrealized loss position for less than 12 months	(5)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	20	43
Fair value, continuous unrealized loss position for 12 months or more	132	358
Unrealized losses, continuous unrealized loss position for 12 months or more	(27)	(77)
Total unrealized losses
Total unrealized losses	(32)	(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	520	132
Fair value, continuous unrealized loss position for less than 12 months	6,594	1,244
Unrealized losses, continuous unrealized loss position for less than 12 months	(299)	(29)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	221	262
Fair value, continuous unrealized loss position for 12 months or more	1,342	1,919
Unrealized losses, continuous unrealized loss position for 12 months or more	(147)	(195)
Total unrealized losses
Total unrealized losses	(446)	(224)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	188	25
Fair value, continuous unrealized loss position for less than 12 months	850	212
Unrealized losses, continuous unrealized loss position for less than 12 months	(34)	(6)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	90	138
Fair value, continuous unrealized loss position for 12 months or more	577	868
Unrealized losses, continuous unrealized loss position for 12 months or more	(94)	(196)
Total unrealized losses
Total unrealized losses	(128)	(202)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	34	3
Fair value, continuous unrealized loss position for less than 12 months	109	57
Unrealized losses, continuous unrealized loss position for less than 12 months	(7)	(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	$ (7)	$ (1)