Investments (Details 10) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 contract	Dec. 31, 2012 contract
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,742	1,234
Fair value, continuous unrealized loss position for less than 12 months	$ 13,881	$ 3,823
Unrealized losses, continuous unrealized loss position for less than 12 months	(387)	(76)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	420	704
Fair value, continuous unrealized loss position for 12 months or more	1,407	3,471
Unrealized losses, continuous unrealized loss position for 12 months or more	(203)	(488)
Total unrealized losses
Total unrealized losses	(590)	(564)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,532	431
Fair value, continuous unrealized loss position for less than 12 months	12,834	3,539
Unrealized losses, continuous unrealized loss position for less than 12 months	(364)	(49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	410	608
Fair value, continuous unrealized loss position for 12 months or more	1,400	3,402
Unrealized losses, continuous unrealized loss position for 12 months or more	(203)	(481)
Total unrealized losses
Total unrealized losses	(567)	(530)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	8	6
Fair value, continuous unrealized loss position for less than 12 months	93	85
Unrealized losses, continuous unrealized loss position for less than 12 months	(2)
Total unrealized losses
Total unrealized losses	(2)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	325	130
Fair value, continuous unrealized loss position for less than 12 months	2,308	1,012
Unrealized losses, continuous unrealized loss position for less than 12 months	(46)	(13)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	33	80
Fair value, continuous unrealized loss position for 12 months or more	191	717
Unrealized losses, continuous unrealized loss position for 12 months or more	(40)	(95)
Total unrealized losses
Total unrealized losses	(86)	(108)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	767	133
Fair value, continuous unrealized loss position for less than 12 months	9,035	1,989
Unrealized losses, continuous unrealized loss position for less than 12 months	(293)	(33)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	44	70
Fair value, continuous unrealized loss position for 12 months or more	467	896
Unrealized losses, continuous unrealized loss position for 12 months or more	(72)	(94)
Total unrealized losses
Total unrealized losses	(365)	(127)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	90	22
Fair value, continuous unrealized loss position for less than 12 months	335	190
Unrealized losses, continuous unrealized loss position for less than 12 months	(11)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	1
Fair value, continuous unrealized loss position for 12 months or more	1
Total unrealized losses
Total unrealized losses	(11)	(1)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	46	12
Fair value, continuous unrealized loss position for less than 12 months	699	145
Unrealized losses, continuous unrealized loss position for less than 12 months	(6)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	42	77
Fair value, continuous unrealized loss position for 12 months or more	407	794
Unrealized losses, continuous unrealized loss position for 12 months or more	(37)	(106)
Total unrealized losses
Total unrealized losses	(43)	(107)
Residential mortgage-backed securities ("RMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	285	117
Fair value, continuous unrealized loss position for less than 12 months	297	50
Unrealized losses, continuous unrealized loss position for less than 12 months	(6)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	280	336
Fair value, continuous unrealized loss position for 12 months or more	261	638
Unrealized losses, continuous unrealized loss position for 12 months or more	(37)	(109)
Total unrealized losses
Total unrealized losses	(43)	(110)
Commercial mortgage-backed securities ("CMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	11	11
Fair value, continuous unrealized loss position for less than 12 months	67	68
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	10	44
Fair value, continuous unrealized loss position for 12 months or more	73	357
Unrealized losses, continuous unrealized loss position for 12 months or more	(17)	(77)
Total unrealized losses
Total unrealized losses	(17)	(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	1,314	387
Fair value, continuous unrealized loss position for less than 12 months	11,320	3,141
Unrealized losses, continuous unrealized loss position for less than 12 months	(306)	(39)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	307	409
Fair value, continuous unrealized loss position for 12 months or more	826	2,172
Unrealized losses, continuous unrealized loss position for 12 months or more	(99)	(217)
Total unrealized losses
Total unrealized losses	(405)	(256)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	218	44
Fair value, continuous unrealized loss position for less than 12 months	1,514	398
Unrealized losses, continuous unrealized loss position for less than 12 months	(58)	(10)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	103	199
Fair value, continuous unrealized loss position for 12 months or more	574	1,230
Unrealized losses, continuous unrealized loss position for 12 months or more	(104)	(264)
Total unrealized losses
Total unrealized losses	(162)	(274)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	210	803
Fair value, continuous unrealized loss position for less than 12 months	1,047	284
Unrealized losses, continuous unrealized loss position for less than 12 months	(23)	(27)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	10	96
Fair value, continuous unrealized loss position for 12 months or more	7	69
Unrealized losses, continuous unrealized loss position for 12 months or more		(7)
Total unrealized losses
Total unrealized losses	$ (23)	$ (34)