Investment Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available for Sale Securities by Type
Cost	$ 4,659	$ 3,158	$ 3,144
Gross Unrealized Gains	10	16	35
Gross Unrealized Losses	(22)	(15)	(22)
Estimated Fair Value	4,647	3,159	3,157
State and municipal obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	594	1,369	2,019
Gross Unrealized Gains	4	11	28
Gross Unrealized Losses	(2)	(3)	(11)
Estimated Fair Value	596	1,377	2,036
U.S. Government agency obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	10	11	12
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Estimated Fair Value	10	11	12
U.S. Government treasury obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	3,452	1,051	465
Gross Unrealized Gains	5	3	3
Gross Unrealized Losses	(17)	(9)	(8)
Estimated Fair Value	3,440	1,045	460
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	28	28	19
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Estimated Fair Value	28	28	19
Mortgage-backed securities [Member]
Schedule of Available for Sale Securities by Type
Cost	50	67	92
Gross Unrealized Gains	1	2	3
Gross Unrealized Losses	0	0	0
Estimated Fair Value	51	69	95
Equity securities [Member]
Schedule of Available for Sale Securities by Type
Cost	51	51	51
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(3)	(3)	(2)
Estimated Fair Value	48	48	49
Foreign government bonds and obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	474	581	486
Gross Unrealized Gains	0	0	1
Gross Unrealized Losses	0	0	(1)
Estimated Fair Value	$ 474	$ 581	$ 486