Investments (Details 10) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 security	Dec. 31, 2012 security
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	699	160
Fair value, continuous unrealized loss position for less than 12 months	$ 5,354	$ 1,513
Unrealized losses, continuous unrealized loss position for less than 12 months	(234)	(36)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	213	401
Fair value, continuous unrealized loss position for 12 months or more	1,162	2,787
Unrealized losses, continuous unrealized loss position for 12 months or more	(163)	(391)
Total unrealized losses
Total unrealized losses	(397)	(427)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	666	157
Fair value, continuous unrealized loss position for less than 12 months	5,260	1,456
Unrealized losses, continuous unrealized loss position for less than 12 months	(229)	(35)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	213	400
Fair value, continuous unrealized loss position for 12 months or more	1,162	2,787
Unrealized losses, continuous unrealized loss position for 12 months or more	(163)	(391)
Total unrealized losses
Gross unrealized losses	(392)	(426)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	3	1
Fair value, continuous unrealized loss position for less than 12 months	51	15
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)
Total unrealized losses
Total unrealized losses	(1)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	50	11
Fair value, continuous unrealized loss position for less than 12 months	281	101
Unrealized losses, continuous unrealized loss position for less than 12 months	(16)	(7)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	22	50
Fair value, continuous unrealized loss position for 12 months or more	136	395
Unrealized losses, continuous unrealized loss position for 12 months or more	(31)	(54)
Total unrealized losses
Total unrealized losses	(47)	(61)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	515	79
Fair value, continuous unrealized loss position for less than 12 months	4,668	1,086
Unrealized losses, continuous unrealized loss position for less than 12 months	(206)	(27)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	41	66
Fair value, continuous unrealized loss position for 12 months or more	428	829
Unrealized losses, continuous unrealized loss position for 12 months or more	(64)	(86)
Total unrealized losses
Total unrealized losses	(270)	(113)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	8	2
Fair value, continuous unrealized loss position for less than 12 months	103	121
Unrealized losses, continuous unrealized loss position for less than 12 months	(4)	(1)
Total unrealized losses
Total unrealized losses	(4)	(1)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	3	5
Fair value, continuous unrealized loss position for less than 12 months	14	38
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	42	76
Fair value, continuous unrealized loss position for 12 months or more	401	763
Unrealized losses, continuous unrealized loss position for 12 months or more	(36)	(105)
Total unrealized losses
Total unrealized losses	(36)	(105)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	79	49
Fair value, continuous unrealized loss position for less than 12 months	82	30
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	99	164
Fair value, continuous unrealized loss position for 12 months or more	124	442
Unrealized losses, continuous unrealized loss position for 12 months or more	(15)	(69)
Total unrealized losses
Total unrealized losses	(17)	(69)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	8	10
Fair value, continuous unrealized loss position for less than 12 months	61	65
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	9	43
Fair value, continuous unrealized loss position for 12 months or more	73	358
Unrealized losses, continuous unrealized loss position for 12 months or more	(17)	(77)
Total unrealized losses
Total unrealized losses	(17)	(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	507	132
Fair value, continuous unrealized loss position for less than 12 months	4,614	1,244
Unrealized losses, continuous unrealized loss position for less than 12 months	(202)	(29)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	155	262
Fair value, continuous unrealized loss position for 12 months or more	806	1,919
Unrealized losses, continuous unrealized loss position for 12 months or more	(98)	(195)
Total unrealized losses
Total unrealized losses	(300)	(224)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	159	25
Fair value, continuous unrealized loss position for less than 12 months	646	212
Unrealized losses, continuous unrealized loss position for less than 12 months	(27)	(6)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	58	138
Fair value, continuous unrealized loss position for 12 months or more	356	868
Unrealized losses, continuous unrealized loss position for 12 months or more	(65)	(196)
Total unrealized losses
Total unrealized losses	(92)	(202)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	33	3
Fair value, continuous unrealized loss position for less than 12 months	94	57
Unrealized losses, continuous unrealized loss position for less than 12 months	(5)	(1)
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	$ (5)	$ (1)