Investments (Details 10) (USD $) In Millions, unless otherwise specified	Jun. 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	1,844	1,234
Fair value, continuous unrealized loss position for less than 12 months	$ 18,344	$ 3,823
Unrealized losses, continuous unrealized loss position for less than 12 months	(613)	(76)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	516	704
Fair value, continuous unrealized loss position for 12 months or more	2,176	3,471
Unrealized losses, continuous unrealized loss position for 12 months or more	(282)	(488)
Total unrealized losses
Total unrealized losses	(895)	(564)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,579	431
Fair value, continuous unrealized loss position for less than 12 months	16,748	3,539
Unrealized losses, continuous unrealized loss position for less than 12 months	(519)	(49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	507	608
Fair value, continuous unrealized loss position for 12 months or more	2,171	3,402
Unrealized losses, continuous unrealized loss position for 12 months or more	(282)	(481)
Total unrealized losses
Total unrealized losses	(801)	(530)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	22	6
Fair value, continuous unrealized loss position for less than 12 months	562	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	334	130
Fair value, continuous unrealized loss position for less than 12 months	2,360	1,012
Unrealized losses, continuous unrealized loss position for less than 12 months	(60)	(13)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	40	80
Fair value, continuous unrealized loss position for 12 months or more	200	717
Unrealized losses, continuous unrealized loss position for 12 months or more	(45)	(95)
Total unrealized losses
Total unrealized losses	(105)	(108)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	827	133
Fair value, continuous unrealized loss position for less than 12 months	12,084	1,989
Unrealized losses, continuous unrealized loss position for less than 12 months	(418)	(33)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	57	70
Fair value, continuous unrealized loss position for 12 months or more	717	896
Unrealized losses, continuous unrealized loss position for 12 months or more	(94)	(94)
Total unrealized losses
Total unrealized losses	(512)	(127)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	93	22
Fair value, continuous unrealized loss position for less than 12 months	434	190
Unrealized losses, continuous unrealized loss position for less than 12 months	(16)	(1)
Total unrealized losses
Total unrealized losses	(16)	(1)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	43	12
Fair value, continuous unrealized loss position for less than 12 months	684	145
Unrealized losses, continuous unrealized loss position for less than 12 months	(8)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	71	77
Fair value, continuous unrealized loss position for 12 months or more	741	794
Unrealized losses, continuous unrealized loss position for 12 months or more	(69)	(106)
Total unrealized losses
Total unrealized losses	(77)	(107)
Residential mortgage-backed securities ("RMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	238	117
Fair value, continuous unrealized loss position for less than 12 months	398	50
Unrealized losses, continuous unrealized loss position for less than 12 months	(10)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	318	336
Fair value, continuous unrealized loss position for 12 months or more	380	638
Unrealized losses, continuous unrealized loss position for 12 months or more	(47)	(109)
Total unrealized losses
Total unrealized losses	(57)	(110)
Commercial mortgage-backed securities ("CMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	22	11
Fair value, continuous unrealized loss position for less than 12 months	226	68
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	21	44
Fair value, continuous unrealized loss position for 12 months or more	133	357
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	1,344	387
Fair value, continuous unrealized loss position for less than 12 months	15,012	3,141
Unrealized losses, continuous unrealized loss position for less than 12 months	(460)	(39)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	373	409
Fair value, continuous unrealized loss position for 12 months or more	1,371	2,172
Unrealized losses, continuous unrealized loss position for 12 months or more	(148)	(217)
Total unrealized losses
Total unrealized losses	(608)	(256)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	235	44
Fair value, continuous unrealized loss position for less than 12 months	1,736	398
Unrealized losses, continuous unrealized loss position for less than 12 months	(59)	(10)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	134	199
Fair value, continuous unrealized loss position for 12 months or more	800	1,230
Unrealized losses, continuous unrealized loss position for 12 months or more	(134)	(264)
Total unrealized losses
Total unrealized losses	(193)	(274)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	265	803
Fair value, continuous unrealized loss position for less than 12 months	1,596	284
Unrealized losses, continuous unrealized loss position for less than 12 months	(94)	(27)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	9	96
Fair value, continuous unrealized loss position for 12 months or more	5	69
Unrealized losses, continuous unrealized loss position for 12 months or more		(7)
Total unrealized losses
Total unrealized losses	$ (94)	$ (34)