Investment Securities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available for Sale Securities by Type
Cost	$ 3,792	$ 3,668
Gross Unrealized Gains	101	100
Gross Unrealized Losses	(1)	(9)
Estimated Fair Value	3,892	3,759
U.S. States and Political Subdivisions Debt Securities [Member]
Schedule of Available for Sale Securities by Type
Cost	2,530	2,813
Gross Unrealized Gains	72	85
Gross Unrealized Losses	0	(5)
Estimated Fair Value	2,602	2,893
U.S. Government agency obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	2	2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2	2
U.S. Government treasury obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	354	406
Gross Unrealized Gains	14	4
Gross Unrealized Losses	0	(1)
Estimated Fair Value	368	409
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	26	29
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Value	27	30
Mortgage-backed securities [Member]
Schedule of Available for Sale Securities by Type
Cost	111	117
Gross Unrealized Gains	5	4
Gross Unrealized Losses	0	0
Estimated Fair Value	116	121
Equity securities [Member]
Schedule of Available for Sale Securities by Type
Cost	1	1
Gross Unrealized Gains	0	0
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	718	250
Gross Unrealized Gains	9	6
Gross Unrealized Losses	0	(1)
Estimated Fair Value	727	255
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)	(2)
Estimated Fair Value	$ 49	$ 48