Investments (Details 10) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Total unrealized losses
Gross unrealized losses	$ (686)	$ (1,670)
Gross unrealized losses on equity securities	(62)	(209)
Total unrealized losses	(748)	(1,879)
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,310	2,206
Fair value, continuous unrealized loss position for less than 12 months	2,360	7,551
Unrealized losses, continuous unrealized loss position for less than 12 months	(89)	(405)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	705	911
Fair value, continuous unrealized loss position for 12 months or more	4,153	5,881
Unrealized losses, continuous unrealized loss position for 12 months or more	(659)	(1,474)
Total unrealized losses
Total unrealized losses	(748)	(1,879)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	418	809
Fair value, continuous unrealized loss position for less than 12 months	1,697	5,431
Unrealized losses, continuous unrealized loss position for less than 12 months	(46)	(202)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	569	879
Fair value, continuous unrealized loss position for 12 months or more	4,073	5,851
Unrealized losses, continuous unrealized loss position for 12 months or more	(640)	(1,468)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	4	4
Fair value, continuous unrealized loss position for less than 12 months	225	61
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	35	29
Fair value, continuous unrealized loss position for less than 12 months	215	135
Unrealized losses, continuous unrealized loss position for less than 12 months	(9)	(11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	117	303
Fair value, continuous unrealized loss position for 12 months or more	1,052	1,886
Unrealized losses, continuous unrealized loss position for 12 months or more	(152)	(245)
Total unrealized losses
Total unrealized losses	(161)	(256)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	79	307
Fair value, continuous unrealized loss position for less than 12 months	919	3,439
Unrealized losses, continuous unrealized loss position for less than 12 months	(30)	(113)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	82	105
Fair value, continuous unrealized loss position for 12 months or more	977	1,273
Unrealized losses, continuous unrealized loss position for 12 months or more	(116)	(266)
Total unrealized losses
Total unrealized losses	(146)	(379)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	7	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	269	321
Fair value, continuous unrealized loss position for less than 12 months	51	373
Unrealized losses, continuous unrealized loss position for less than 12 months	(3)	(11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	236	294
Fair value, continuous unrealized loss position for 12 months or more	735	1,182
Unrealized losses, continuous unrealized loss position for 12 months or more	(143)	(510)
Total unrealized losses
Total unrealized losses	(146)	(521)
Commercial mortgage-backed securities ("CMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	4	47
Fair value, continuous unrealized loss position for less than 12 months	21	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	50	68
Fair value, continuous unrealized loss position for 12 months or more	449	489
Unrealized losses, continuous unrealized loss position for 12 months or more	(91)	(177)
Total unrealized losses
Total unrealized losses	(91)	(226)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	19	89
Fair value, continuous unrealized loss position for less than 12 months	249	960
Unrealized losses, continuous unrealized loss position for less than 12 months	(4)	(17)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	83	108
Fair value, continuous unrealized loss position for 12 months or more	859	1,020
Unrealized losses, continuous unrealized loss position for 12 months or more	(138)	(270)
Total unrealized losses
Total unrealized losses	(142)	(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	364	665
Fair value, continuous unrealized loss position for less than 12 months	1,275	4,480
Unrealized losses, continuous unrealized loss position for less than 12 months	(30)	(145)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	346	555
Fair value, continuous unrealized loss position for 12 months or more	2,584	3,773
Unrealized losses, continuous unrealized loss position for 12 months or more	(293)	(700)
Total unrealized losses
Total unrealized losses	(323)	(845)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	54	144
Fair value, continuous unrealized loss position for less than 12 months	422	951
Unrealized losses, continuous unrealized loss position for less than 12 months	(16)	(57)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	223	324
Fair value, continuous unrealized loss position for 12 months or more	1,489	2,078
Unrealized losses, continuous unrealized loss position for 12 months or more	(347)	(768)
Total unrealized losses
Total unrealized losses	(363)	(825)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	892	1,397
Fair value, continuous unrealized loss position for less than 12 months	663	2,120
Unrealized losses, continuous unrealized loss position for less than 12 months	(43)	(203)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	136	32
Fair value, continuous unrealized loss position for 12 months or more	80	30
Unrealized losses, continuous unrealized loss position for 12 months or more	$ (19)	$ (6)