Investment Securities (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available for Sale Securities by Type
Cost	$ 3,838	$ 4,280
Gross Unrealized Gains	115	154
Gross Unrealized Losses	(6)	(3)
Estimated Fair Value	3,947	4,431
U.S. States and Political Subdivisions Debt Securities [Member]
Schedule of Available for Sale Securities by Type
Cost	2,971	3,366
Gross Unrealized Gains	97	129
Gross Unrealized Losses	(4)	(2)
Estimated Fair Value	3,064	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	297	346
Gross Unrealized Gains	5	4
Gross Unrealized Losses	0	0
Estimated Fair Value	302	350
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	30	37
Gross Unrealized Gains	1	3
Gross Unrealized Losses	0	0
Estimated Fair Value	31	40
Mortgage-backed securities [Member]
Schedule of Available for Sale Securities by Type
Cost	109	128
Gross Unrealized Gains	5	8
Gross Unrealized Losses	0	0
Estimated Fair Value	114	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	379	350
Gross Unrealized Gains	6	9
Gross Unrealized Losses	(1)	0
Estimated Fair Value	384	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	(1)	(1)
Estimated Fair Value	$ 49	$ 49