Investments (Details 10) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012 security	Dec. 31, 2011 security
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	199	459
Fair value, continuous unrealized loss position for less than 12 months	$ 867	$ 2,936
Unrealized losses, continuous unrealized loss position for less than 12 months	(33)	(146)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	387	534
Fair value, continuous unrealized loss position for 12 months or more	3,116	4,139
Unrealized losses, continuous unrealized loss position for 12 months or more	(495)	(1,116)
Total unrealized losses
Total unrealized losses	(528)	(1,262)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	196	456
Fair value, continuous unrealized loss position for less than 12 months	849	2,901
Unrealized losses, continuous unrealized loss position for less than 12 months	(33)	(144)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	386	534
Fair value, continuous unrealized loss position for 12 months or more	3,116	4,139
Unrealized losses, continuous unrealized loss position for 12 months or more	(495)	(1,116)
Total unrealized losses
Gross unrealized losses	(528)	(1,260)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	10	8
Fair value, continuous unrealized loss position for less than 12 months	84	67
Unrealized losses, continuous unrealized loss position for less than 12 months	(7)	(7)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	61	97
Fair value, continuous unrealized loss position for 12 months or more	468	624
Unrealized losses, continuous unrealized loss position for 12 months or more	(67)	(107)
Total unrealized losses
Total unrealized losses	(74)	(114)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	61	226
Fair value, continuous unrealized loss position for less than 12 months	639	2,025
Unrealized losses, continuous unrealized loss position for less than 12 months	(23)	(72)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	77	100
Fair value, continuous unrealized loss position for 12 months or more	910	1,207
Unrealized losses, continuous unrealized loss position for 12 months or more	(107)	(254)
Total unrealized losses
Total unrealized losses	(130)	(326)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months		7
Fair value, continuous unrealized loss position for less than 12 months		41
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)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	110	140
Fair value, continuous unrealized loss position for less than 12 months	30	152
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)	(4)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	118	161
Fair value, continuous unrealized loss position for 12 months or more	510	809
Unrealized losses, continuous unrealized loss position for 12 months or more	(95)	(310)
Total unrealized losses
Total unrealized losses	(96)	(314)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	4	42
Fair value, continuous unrealized loss position for less than 12 months	21	361
Unrealized losses, continuous unrealized loss position for less than 12 months		(47)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	49	68
Fair value, continuous unrealized loss position for 12 months or more	448	488
Unrealized losses, continuous unrealized loss position for 12 months or more	(91)	(177)
Total unrealized losses
Total unrealized losses	(91)	(224)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	10	32
Fair value, continuous unrealized loss position for less than 12 months	75	255
Unrealized losses, continuous unrealized loss position for less than 12 months	(2)	(13)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	80	107
Fair value, continuous unrealized loss position for 12 months or more	779	1,010
Unrealized losses, continuous unrealized loss position for 12 months or more	(135)	(268)
Total unrealized losses
Total unrealized losses	(137)	(281)
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	162	351
Fair value, continuous unrealized loss position for less than 12 months	620	2,439
Unrealized losses, continuous unrealized loss position for less than 12 months	(25)	(111)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	233	328
Fair value, continuous unrealized loss position for 12 months or more	2,164	2,869
Unrealized losses, continuous unrealized loss position for 12 months or more	(258)	(626)
Total unrealized losses
Total unrealized losses	(283)	(737)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	34	105
Fair value, continuous unrealized loss position for less than 12 months	229	462
Unrealized losses, continuous unrealized loss position for less than 12 months	(8)	(33)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	153	206
Fair value, continuous unrealized loss position for 12 months or more	952	1,270
Unrealized losses, continuous unrealized loss position for 12 months or more	(237)	(490)
Total unrealized losses
Total unrealized losses	(245)	(523)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	3	3
Fair value, continuous unrealized loss position for less than 12 months	18	35
Unrealized losses, continuous unrealized loss position for less than 12 months		(2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	1
Total unrealized losses
Gross unrealized losses on equity securities		$ (2)