Investments (Details 10) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Total unrealized losses
Gross unrealized losses	$ (530)	$ (1,670)
Gross unrealized losses on equity securities	(34)	(209)
Total unrealized losses	(564)	(1,879)
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,234	2,206
Fair value, continuous unrealized loss position for less than 12 months	3,823	7,551
Unrealized losses, continuous unrealized loss position for less than 12 months	(76)	(405)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	704	911
Fair value, continuous unrealized loss position for 12 months or more	3,471	5,881
Unrealized losses, continuous unrealized loss position for 12 months or more	(488)	(1,474)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	431	809
Fair value, continuous unrealized loss position for less than 12 months	3,539	5,431
Unrealized losses, continuous unrealized loss position for less than 12 months	(49)	(202)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	608	879
Fair value, continuous unrealized loss position for 12 months or more	3,402	5,851
Unrealized losses, continuous unrealized loss position for 12 months or more	(481)	(1,468)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	6	4
Fair value, continuous unrealized loss position for less than 12 months	85	61
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	130	29
Fair value, continuous unrealized loss position for less than 12 months	1,012	135
Unrealized losses, continuous unrealized loss position for less than 12 months	(13)	(11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	80	303
Fair value, continuous unrealized loss position for 12 months or more	717	1,886
Unrealized losses, continuous unrealized loss position for 12 months or more	(95)	(245)
Total unrealized losses
Total unrealized losses	(108)	(256)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	133	307
Fair value, continuous unrealized loss position for less than 12 months	1,989	3,439
Unrealized losses, continuous unrealized loss position for less than 12 months	(33)	(113)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	70	105
Fair value, continuous unrealized loss position for 12 months or more	896	1,273
Unrealized losses, continuous unrealized loss position for 12 months or more	(94)	(266)
Total unrealized losses
Total unrealized losses	(127)	(379)
Foreign government
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	190	85
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
Fair value, continuous unrealized loss position for 12 months or more		1
Total unrealized losses
Total unrealized losses	(1)	(1)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	12	89
Fair value, continuous unrealized loss position for less than 12 months	145	960
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)	(17)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	77	108
Fair value, continuous unrealized loss position for 12 months or more	794	1,020
Unrealized losses, continuous unrealized loss position for 12 months or more	(106)	(270)
Total unrealized losses
Total unrealized losses	(107)	(287)
Residential mortgage-backed securities ("RMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	117	321
Fair value, continuous unrealized loss position for less than 12 months	50	373
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)	(11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	336	294
Fair value, continuous unrealized loss position for 12 months or more	638	1,182
Unrealized losses, continuous unrealized loss position for 12 months or more	(109)	(510)
Total unrealized losses
Total unrealized losses	(110)	(521)
Commercial mortgage-backed securities ("CMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	11	47
Fair value, continuous unrealized loss position for less than 12 months	68	378
Unrealized losses, continuous unrealized loss position for less than 12 months		(49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	44	68
Fair value, continuous unrealized loss position for 12 months or more	357	489
Unrealized losses, continuous unrealized loss position for 12 months or more	(77)	(177)
Total unrealized losses
Total unrealized losses	(77)	(226)
Redeemable preferred stock
Less than 12 months
Number of issues, 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	1
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	387	665
Fair value, continuous unrealized loss position for less than 12 months	3,141	4,480
Unrealized losses, continuous unrealized loss position for less than 12 months	(39)	(145)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	409	555
Fair value, continuous unrealized loss position for 12 months or more	2,172	3,773
Unrealized losses, continuous unrealized loss position for 12 months or more	(217)	(700)
Total unrealized losses
Total unrealized losses	(256)	(845)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	44	144
Fair value, continuous unrealized loss position for less than 12 months	398	951
Unrealized losses, continuous unrealized loss position for less than 12 months	(10)	(57)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	199	324
Fair value, continuous unrealized loss position for 12 months or more	1,230	2,078
Unrealized losses, continuous unrealized loss position for 12 months or more	(264)	(768)
Total unrealized losses
Total unrealized losses	(274)	(825)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	803	1,397
Fair value, continuous unrealized loss position for less than 12 months	284	2,120
Unrealized losses, continuous unrealized loss position for less than 12 months	(27)	(203)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	96	32
Fair value, continuous unrealized loss position for 12 months or more	69	30
Unrealized losses, continuous unrealized loss position for 12 months or more	$ (7)	$ (6)