Investments and Cash - Gross Unrealized Loss by Length of Time (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015 Security		Dec. 31, 2014 Security
Less than 12 months
Fair value	$ 680		$ 797
Unrealized loss	(17)		(10)
12 months or more
Fair Value	109		393
Unrealized loss	(15)		(23)
Total
Fair value	789		1,190
Unrealized loss	(32)		(33)
Number of securities
Less than 12 months (in securities)	166	[1]	125	[1]
12 months or more (in securities)	24	[1]	82	[1]
Total (in securities)	187	[1]	198	[1]
Number of securities with OTTI
Less than 12 months (in securities)	2		3
12 months or more (in securities)	3		7
Total (in securities)	5		10
Obligations of state and political subdivisions [Member]
Less than 12 months
Fair value	189		64
Unrealized loss	(2)		0
12 months or more
Fair Value	5		25
Unrealized loss	0		(1)
Total
Fair value	194		89
Unrealized loss	(2)		(1)
US Treasury and Government [Member]
Less than 12 months
Fair value	26		139
Unrealized loss	0		0
12 months or more
Fair Value	12		68
Unrealized loss	0		(1)
Total
Fair value	38		207
Unrealized loss	0		(1)
Corporate securities [Member]
Less than 12 months
Fair value	194		189
Unrealized loss	(6)		(3)
12 months or more
Fair Value	5		104
Unrealized loss	0		(2)
Total
Fair value	199		293
Unrealized loss	(6)		(5)
RMBS [Member]
Less than 12 months
Fair value	94		205
Unrealized loss	(1)		(3)
12 months or more
Fair Value	85		159
Unrealized loss	(15)		(18)
Total
Fair value	179		364
Unrealized loss	(16)		(21)
CMBS [Member]
Less than 12 months
Fair value	21		36
Unrealized loss	0		0
12 months or more
Fair Value	2		19
Unrealized loss	0		0
Total
Fair value	23		55
Unrealized loss	0		0
Asset-backed Securities [Member]
Less than 12 months
Fair value	0		56
Unrealized loss	0		(2)
12 months or more
Fair Value	0		18
Unrealized loss	0		(1)
Total
Fair value	0		74
Unrealized loss	0		(3)
Foreign government securities [Member]
Less than 12 months
Fair value	156		108
Unrealized loss	(8)		(2)
12 months or more
Fair Value	0		0
Unrealized loss	0		0
Total
Fair value	156		108
Unrealized loss	$ (8)		$ (2)

[1] The number of securities does not add across because lots of the same securities 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.