Investments and Cash (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Security	Dec. 31, 2012 Security
Less than 12 months
Fair value	$ 558	$ 303
Unrealized loss	(30)	(30)
12 months or more
Fair Value	137	156
Unrealized loss	(61)	(68)
Total
Fair value	695	459
Unrealized loss	(91)	(98)
Number of securities
Less than 12 months (in securities)	105	58
12 months or more (in securities)	12	16
Total (in securities)	117	74
Number of securities with OTTI
Less than 12 months (in securities)	5	5
12 months or more (in securities)	5	6
Total (in securities)	10	11
Number of securities with unrealized losses greater than 10% of book value for 12 months or more	8
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	60
U.S. government and agencies
Less than 12 months
Fair value	43	62
Unrealized loss	0	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Fair value	43	62
Unrealized loss	0	0
Obligations of state and political subdivisions
Less than 12 months
Fair value	158	79
Unrealized loss	(12)	(11)
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Fair value	158	79
Unrealized loss	(12)	(11)
Corporate securities
Less than 12 months
Fair value	76	25
Unrealized loss	(1)	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Fair value	76	25
Unrealized loss	(1)	0
RMBS
Less than 12 months
Fair value	184	108
Unrealized loss	(15)	(19)
12 months or more
Fair Value	99	121
Unrealized loss	(53)	(58)
Total
Fair value	283	229
Unrealized loss	(68)	(77)
CMBS
Less than 12 months
Fair value	16	5
Unrealized loss	0	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Fair value	16	5
Unrealized loss	0	0
Asset-backed securities
Less than 12 months
Fair value	19	16
Unrealized loss	0	0
12 months or more
Fair Value	38	35
Unrealized loss	(8)	(10)
Total
Fair value	57	51
Unrealized loss	(8)	(10)
Foreign government securities
Less than 12 months
Fair value	62	8
Unrealized loss	(2)	0
12 months or more
Fair Value	0	0
Unrealized loss	0	0
Total
Fair value	62	8
Unrealized loss	$ (2)	$ 0