Investment Securities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available for Sale Securities by Type
Cost	$ 4,465	$ 4,280
Gross Unrealized Gains	123	154
Gross Unrealized Losses	(4)	(3)
Estimated Fair Value	4,584	4,431
U.S. States and Political Subdivisions Debt Securities [Member]
Schedule of Available for Sale Securities by Type
Cost	3,076	3,366
Gross Unrealized Gains	101	129
Gross Unrealized Losses	(2)	(2)
Estimated Fair Value	3,175	3,493
U.S. Government agency obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	2	3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2	3
U.S. Government treasury obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	345	346
Gross Unrealized Gains	6	4
Gross Unrealized Losses	0	0
Estimated Fair Value	351	350
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	37	37
Gross Unrealized Gains	2	3
Gross Unrealized Losses	0	0
Estimated Fair Value	39	40
Mortgage-backed securities [Member]
Schedule of Available for Sale Securities by Type
Cost	115	128
Gross Unrealized Gains	5	8
Gross Unrealized Losses	0	0
Estimated Fair Value	120	136
Equity securities [Member]
Schedule of Available for Sale Securities by Type
Cost	0	0
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Value	1	1
Foreign government bonds and obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	840	350
Gross Unrealized Gains	8	9
Gross Unrealized Losses	0	0
Estimated Fair Value	848	359
Availabe For Sale Securities Other [Member]
Schedule of Available for Sale Securities by Type
Cost	50	50
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(1)
Estimated Fair Value	$ 48	$ 49