Investments and Cash - Gross Unrealized Loss by Length of Time (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 Security		Dec. 31, 2013 Security
Less than 12 months
Fair value	$ 797		$ 2,140
Unrealized loss	(10)		(91)
12 months or more
Fair Value	393		237
Unrealized loss	(23)		(56)
Total
Fair value	1,190		2,377
Unrealized loss	(33)		(147)
Number of securities
Less than 12 months (in securities)	125	[1]	425
12 months or more (in securities)	82	[1]	33
Total (in securities)	198	[1]	458
Number of securities with OTTI
Less than 12 months (in securities)	3		13
12 months or more (in securities)	7		11
Total (in securities)	10		24
Obligations of state and political subdivisions [Member]
Less than 12 months
Fair value	64		781
Unrealized loss	0		(39)
12 months or more
Fair Value	25		5
Unrealized loss	(1)		0
Total
Fair value	89		786
Unrealized loss	(1)		(39)
US Treasury and Government [Member]
Less than 12 months
Fair value	139		173
Unrealized loss	0		(6)
12 months or more
Fair Value	68		0
Unrealized loss	(1)		0
Total
Fair value	207		173
Unrealized loss	(1)		(6)
Corporate securities [Member]
Less than 12 months
Fair value	189		401
Unrealized loss	(3)		(18)
12 months or more
Fair Value	104		3
Unrealized loss	(2)		0
Total
Fair value	293		404
Unrealized loss	(5)		(18)
RMBS [Member]
Less than 12 months
Fair value	205		414
Unrealized loss	(3)		(21)
12 months or more
Fair Value	159		186
Unrealized loss	(18)		(51)
Total
Fair value	364		600
Unrealized loss	(21)		(72)
CMBS [Member]
Less than 12 months
Fair value	36		121
Unrealized loss	0		(4)
12 months or more
Fair Value	19		0
Unrealized loss	0		0
Total
Fair value	55		121
Unrealized loss	0		(4)
Asset-backed Securities [Member]
Less than 12 months
Fair value	56		196
Unrealized loss	(2)		(2)
12 months or more
Fair Value	18		42
Unrealized loss	(1)		(5)
Total
Fair value	74		238
Unrealized loss	(3)		(7)
Foreign government securities [Member]
Less than 12 months
Fair value	108		54
Unrealized loss	(2)		(1)
12 months or more
Fair Value	0		1
Unrealized loss	0		0
Total
Fair value	108		55
Unrealized loss	$ (2)		$ (1)

[1] The number of securities does not add across because of lots of the same securities that have been purchased at different times and appear in both categories above (i.e., Less than 12 months and 12 months or more). If a security appears in both categories, it is counted only once in the Total column.