Investments (Details 10) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Total unrealized losses
Gross unrealized losses	$ (382)	$ (530)
Gross unrealized losses on equity securities	(15)	(34)
Total unrealized losses	(397)	(564)
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	977	1,234
Fair value, continuous unrealized loss position for less than 12 months	4,504	3,823
Unrealized losses, continuous unrealized loss position for less than 12 months	(63)	(76)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	608	704
Fair value, continuous unrealized loss position for 12 months or more	2,689	3,471
Unrealized losses, continuous unrealized loss position for 12 months or more	(334)	(488)
Total unrealized losses
Total unrealized losses	(397)	(564)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	488	431
Fair value, continuous unrealized loss position for less than 12 months	4,377	3,539
Unrealized losses, continuous unrealized loss position for less than 12 months	(51)	(49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	560	608
Fair value, continuous unrealized loss position for 12 months or more	2,661	3,402
Unrealized losses, continuous unrealized loss position for 12 months or more	(331)	(481)
Total unrealized losses
Total unrealized losses	(382)	(530)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	6	6
Fair value, continuous unrealized loss position for less than 12 months	229	85
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	102	130
Fair value, continuous unrealized loss position for less than 12 months	709	1,012
Unrealized losses, continuous unrealized loss position for less than 12 months	(8)	(13)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	44	80
Fair value, continuous unrealized loss position for 12 months or more	242	717
Unrealized losses, continuous unrealized loss position for 12 months or more	(38)	(95)
Total unrealized losses
Total unrealized losses	(46)	(108)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	197	133
Fair value, continuous unrealized loss position for less than 12 months	2,845	1,989
Unrealized losses, continuous unrealized loss position for less than 12 months	(38)	(33)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	66	70
Fair value, continuous unrealized loss position for 12 months or more	841	896
Unrealized losses, continuous unrealized loss position for 12 months or more	(90)	(94)
Total unrealized losses
Total unrealized losses	(128)	(127)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	18	22
Fair value, continuous unrealized loss position for less than 12 months	170	190
Unrealized losses, continuous unrealized loss position for less than 12 months	(3)	(1)
Total unrealized losses
Total unrealized losses	(3)	(1)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	17	12
Fair value, continuous unrealized loss position for less than 12 months	332	145
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	76	77
Fair value, continuous unrealized loss position for 12 months or more	799	794
Unrealized losses, continuous unrealized loss position for 12 months or more	(86)	(106)
Total unrealized losses
Total unrealized losses	(86)	(107)
Residential mortgage-backed securities ("RMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	141	117
Fair value, continuous unrealized loss position for less than 12 months	34	50
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	346	336
Fair value, continuous unrealized loss position for 12 months or more	549	638
Unrealized losses, continuous unrealized loss position for 12 months or more	(76)	(109)
Total unrealized losses
Total unrealized losses	(77)	(110)
Commercial mortgage-backed securities ("CMBS")
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	58	68
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	28	44
Fair value, continuous unrealized loss position for 12 months or more	230	357
Unrealized losses, continuous unrealized loss position for 12 months or more	(41)	(77)
Total unrealized losses
Total unrealized losses	(42)	(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	412	387
Fair value, continuous unrealized loss position for less than 12 months	3,878	3,141
Unrealized losses, continuous unrealized loss position for less than 12 months	(39)	(39)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	395	409
Fair value, continuous unrealized loss position for 12 months or more	1,620	2,172
Unrealized losses, continuous unrealized loss position for 12 months or more	(148)	(217)
Total unrealized losses
Total unrealized losses	(187)	(256)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	76	44
Fair value, continuous unrealized loss position for less than 12 months	499	398
Unrealized losses, continuous unrealized loss position for less than 12 months	(12)	(10)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	165	199
Fair value, continuous unrealized loss position for 12 months or more	1,041	1,230
Unrealized losses, continuous unrealized loss position for 12 months or more	(183)	(264)
Total unrealized losses
Total unrealized losses	(195)	(274)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	489	803
Fair value, continuous unrealized loss position for less than 12 months	127	284
Unrealized losses, continuous unrealized loss position for less than 12 months	(12)	(27)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	48	96
Fair value, continuous unrealized loss position for 12 months or more	28	69
Unrealized losses, continuous unrealized loss position for 12 months or more	(3)	(7)
Total unrealized losses
Total unrealized losses	$ (15)	$ (34)