Investments and Cash (Details 3) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 Security	Dec. 31, 2012 Security
Less than 12 months
Fair value	$ 1,854	$ 303
Unrealized loss	(74)	(30)
12 months or more
Fair Value	210	156
Unrealized loss	(64)	(68)
Total
Total Fair value	2,064	459
Total Unrealized loss	(138)	(98)
Number of securities
Less than 12 months (in securities)	385	58
12 months or more (in securities)	18	16
Total (in securities)	403	74
Number of securities with OTTI
Less than 12 months (in securities)	11	5
12 months or more (in securities)	10	6
Total (in securities)	21	11
Number of securities with unrealized losses greater than 10% of book value for 12 months or more	11
Threshold for measuring unrealized losses for securities as a percent of book value	10.00%
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	63
U.S. government and agencies
Less than 12 months
Fair value	175	62
Unrealized loss	(4)	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Total Fair value	175	62
Total Unrealized loss	(4)	0
Obligations of state and political subdivisions
Less than 12 months
Fair value	731	79
Unrealized loss	(39)	(11)
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Total Fair value	731	79
Total Unrealized loss	(39)	(11)
Corporate securities
Less than 12 months
Fair value	341	25
Unrealized loss	(13)	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Total Fair value	341	25
Total Unrealized loss	(13)	0
RMBS
Less than 12 months
Fair value	373	108
Unrealized loss	(13)	(19)
12 months or more
Fair Value	170	121
Unrealized loss	(57)	(58)
Total
Total Fair value	543	229
Total Unrealized loss	(70)	(77)
CMBS
Less than 12 months
Fair value	59	5
Unrealized loss	(3)	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Total Fair value	59	5
Total Unrealized loss	(3)	0
Asset-backed securities
Less than 12 months
Fair value	117	16
Unrealized loss	(2)	0
12 months or more
Fair Value	40	35
Unrealized loss	(7)	(10)
Total
Total Fair value	157	51
Total Unrealized loss	(9)	(10)
Foreign government securities
Less than 12 months
Fair value	58	8
Unrealized loss	0	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Total Fair value	58	8
Total Unrealized loss	$ 0	$ 0