Investments (Details 10) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Total unrealized losses
Gross unrealized losses	$ (1,128)	$ (1,670)
Gross unrealized losses on equity securities	(110)	(209)
Total unrealized losses	(1,238)	(1,879)
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,903	2,206
Fair value, continuous unrealized loss position for less than 12 months	5,078	7,551
Unrealized losses, continuous unrealized loss position for less than 12 months	(199)	(405)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	763	911
Fair value, continuous unrealized loss position for 12 months or more	4,814	5,881
Unrealized losses, continuous unrealized loss position for 12 months or more	(1,039)	(1,474)
Total unrealized losses
Total unrealized losses	(1,238)	(1,879)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	640	809
Fair value, continuous unrealized loss position for less than 12 months	3,710	5,431
Unrealized losses, continuous unrealized loss position for less than 12 months	(106)	(202)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	675	879
Fair value, continuous unrealized loss position for 12 months or more	4,761	5,851
Unrealized losses, continuous unrealized loss position for 12 months or more	(1,022)	(1,468)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	5	4
Fair value, continuous unrealized loss position for less than 12 months	185	61
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	98	29
Fair value, continuous unrealized loss position for less than 12 months	733	135
Unrealized losses, continuous unrealized loss position for less than 12 months	(12)	(11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	146	303
Fair value, continuous unrealized loss position for 12 months or more	1,189	1,886
Unrealized losses, continuous unrealized loss position for 12 months or more	(174)	(245)
Total unrealized losses
Total unrealized losses	(186)	(256)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	179	307
Fair value, continuous unrealized loss position for less than 12 months	2,080	3,439
Unrealized losses, continuous unrealized loss position for less than 12 months	(68)	(113)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	84	105
Fair value, continuous unrealized loss position for 12 months or more	1,042	1,273
Unrealized losses, continuous unrealized loss position for 12 months or more	(158)	(266)
Total unrealized losses
Total unrealized losses	(226)	(379)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	4	11
Fair value, continuous unrealized loss position for less than 12 months	17	85
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	1	1
Fair value, continuous unrealized loss position for 12 months or more	1	1
Total unrealized losses
Total unrealized losses		(1)
Residential mortgage-backed securities ("RMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	298	321
Fair value, continuous unrealized loss position for less than 12 months	42	373
Unrealized losses, continuous unrealized loss position for less than 12 months	(2)	(11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	284	294
Fair value, continuous unrealized loss position for 12 months or more	1,045	1,182
Unrealized losses, continuous unrealized loss position for 12 months or more	(328)	(510)
Total unrealized losses
Total unrealized losses	(330)	(521)
Commercial mortgage-backed securities ("CMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	18	47
Fair value, continuous unrealized loss position for less than 12 months	109	378
Unrealized losses, continuous unrealized loss position for less than 12 months	(4)	(49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	70	68
Fair value, continuous unrealized loss position for 12 months or more	572	489
Unrealized losses, continuous unrealized loss position for 12 months or more	(167)	(177)
Total unrealized losses
Total unrealized losses	(171)	(226)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	37	89
Fair value, continuous unrealized loss position for less than 12 months	544	960
Unrealized losses, continuous unrealized loss position for less than 12 months	(20)	(17)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	90	108
Fair value, continuous unrealized loss position for 12 months or more	912	1,020
Unrealized losses, continuous unrealized loss position for 12 months or more	(195)	(270)
Total unrealized losses
Total unrealized losses	(215)	(287)
Redeemable preferred stock
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1	1
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	538	665
Fair value, continuous unrealized loss position for less than 12 months	2,868	4,480
Unrealized losses, continuous unrealized loss position for less than 12 months	(56)	(145)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	395	555
Fair value, continuous unrealized loss position for 12 months or more	2,807	3,773
Unrealized losses, continuous unrealized loss position for 12 months or more	(437)	(700)
Total unrealized losses
Total unrealized losses	(493)	(845)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	102	144
Fair value, continuous unrealized loss position for less than 12 months	842	951
Unrealized losses, continuous unrealized loss position for less than 12 months	(50)	(57)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	280	324
Fair value, continuous unrealized loss position for 12 months or more	1,954	2,078
Unrealized losses, continuous unrealized loss position for 12 months or more	(585)	(768)
Total unrealized losses
Total unrealized losses	(635)	(825)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,263	1,397
Fair value, continuous unrealized loss position for less than 12 months	1,368	2,120
Unrealized losses, continuous unrealized loss position for less than 12 months	(93)	(203)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	88	32
Fair value, continuous unrealized loss position for 12 months or more	53	30
Unrealized losses, continuous unrealized loss position for 12 months or more	$ (17)	$ (6)