Investments and Cash - Gross Unrealized Loss by Length of Time (Details) $ in Millions		Jun. 30, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security
Less than 12 months
Fair value		$ 2,285	$ 797
Unrealized loss		(51)	(10)
12 months or more
Fair Value		189	393
Unrealized loss		(18)	(23)
Total
Fair value		2,474	1,190
Unrealized loss		$ (69)	$ (33)
Number of securities
Less than 12 months (in securities) | Security	[1]	527	125
12 months or more (in securities) | Security	[1]	26	82
Total (in securities) | Security	[1]	550	198
Number of securities with OTTI
Less than 12 months (in securities) | Security		4	3
12 months or more (in securities) | Security		4	7
Total (in securities) | Security		8	10
Obligations of state and political subdivisions [Member]
Less than 12 months
Fair value		$ 1,142	$ 64
Unrealized loss		(28)	0
12 months or more
Fair Value		4	25
Unrealized loss		0	(1)
Total
Fair value		1,146	89
Unrealized loss		(28)	(1)
US Treasury and Government [Member]
Less than 12 months
Fair value		95	139
Unrealized loss		(1)	0
12 months or more
Fair Value		12	68
Unrealized loss		0	(1)
Total
Fair value		107	207
Unrealized loss		(1)	(1)
Corporate securities [Member]
Less than 12 months
Fair value		390	189
Unrealized loss		(11)	(3)
12 months or more
Fair Value		92	104
Unrealized loss		(4)	(2)
Total
Fair value		482	293
Unrealized loss		(15)	(5)
RMBS [Member]
Less than 12 months
Fair value		457	205
Unrealized loss		(8)	(3)
12 months or more
Fair Value		79	159
Unrealized loss		(14)	(18)
Total
Fair value		536	364
Unrealized loss		(22)	(21)
CMBS [Member]
Less than 12 months
Fair value		96	36
Unrealized loss		(1)	0
12 months or more
Fair Value		2	19
Unrealized loss		0	0
Total
Fair value		98	55
Unrealized loss		(1)	0
Asset-backed Securities [Member]
Less than 12 months
Fair value		7	56
Unrealized loss		0	(2)
12 months or more
Fair Value		0	18
Unrealized loss		0	(1)
Total
Fair value		7	74
Unrealized loss		0	(3)
Foreign government securities [Member]
Less than 12 months
Fair value		98	108
Unrealized loss		(2)	(2)
12 months or more
Fair Value		0	0
Unrealized loss		0	0
Total
Fair value		98	108
Unrealized loss		$ (2)	$ (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.