Investment Securities (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Estimated Fair Value
Estimated Fair Value, Due within 1 year	$ 625
Estimated Fair Value, Due after 1 year but within 5 years	994
Estimated Fair Value, Due after 5 years but within 10 years	223
Estimated Fair Value, Due after 10 years	1,269
Total	3,111	$ 3,108
Available For Sale Securities Debt Maturities Amortized Cost [Abstract]
Due within 1 year	625
Due after 1 year but within 5 years	1,000
Due after 5 years but within 10 years	222
Due after 10 years	1,260
Total	$ 3,107
Weighted average yields
Weighted average yields, due within 1 year	3.65%
Weighted averge yields, due after 1 years but within 5 years	1.95%
Weighted averge yields, due after 5 years but within 10 years	4.39%
Weighted average yield, due after 10 years	4.47%
Weighted average yields, Total	3.49%
State and municipal obligations [Member]
Estimated Fair Value
Estimated Fair Value, Due within 1 year	$ 18
Estimated Fair Value, Due after 1 year but within 5 years	87
Estimated Fair Value, Due after 5 years but within 10 years	98
Estimated Fair Value, Due after 10 years	1,174
Total	1,377
U.S. Government treasury obligations [Member]
Estimated Fair Value
Estimated Fair Value, Due within 1 year	0
Estimated Fair Value, Due after 1 year but within 5 years	0
Estimated Fair Value, Due after 5 years but within 10 years	0
Estimated Fair Value, Due after 10 years	11
Total	11
U.S. Government agency obligations [Member]
Estimated Fair Value
Estimated Fair Value, Due within 1 year	30
Estimated Fair Value, Due after 1 year but within 5 years	879
Estimated Fair Value, Due after 5 years but within 10 years	125
Estimated Fair Value, Due after 10 years	11
Total	1,045
Corporate debt securities [Member]
Estimated Fair Value
Estimated Fair Value, Due within 1 year	4
Estimated Fair Value, Due after 1 year but within 5 years	24
Estimated Fair Value, Due after 5 years but within 10 years	0
Estimated Fair Value, Due after 10 years	0
Total	28
Mortgage-backed securities [Member]
Estimated Fair Value
Estimated Fair Value, Due within 1 year	0
Estimated Fair Value, Due after 1 year but within 5 years	0
Estimated Fair Value, Due after 5 years but within 10 years	0
Estimated Fair Value, Due after 10 years	69
Total	69
Foreign government bonds and obligations [Member]
Estimated Fair Value
Estimated Fair Value, Due within 1 year	573
Estimated Fair Value, Due after 1 year but within 5 years	4
Estimated Fair Value, Due after 5 years but within 10 years	0
Estimated Fair Value, Due after 10 years	4
Total	$ 581