Investment Securities Taxable and Nontaxable Interest Income by Investment Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Noninterest Income	$ 84	$ 48	$ 162	$ 95
Taxable [Member]
Noninterest Income	74	42	143	84
Nontaxable [Member]
Noninterest Income	10	6	19	11
Held-to-maturity Securities [Member]
Noninterest Income	5	6	12	11
Held-to-maturity Securities [Member] | Taxable [Member]
Noninterest Income	2	3	5	5
Held-to-maturity Securities [Member] | Nontaxable [Member]
Noninterest Income	3	3	7	6
Available-for-sale Securities [Member]
Noninterest Income	78	41	149	83
Available-for-sale Securities [Member] | Taxable [Member]
Noninterest Income	71	38	137	78
Available-for-sale Securities [Member] | Nontaxable [Member]
Noninterest Income	7	3	12	5
Trading Securities [Member]
Noninterest Income	1	1	1	1
Trading Securities [Member] | Taxable [Member]
Noninterest Income	1	1	1	1
Trading Securities [Member] | Nontaxable [Member]
Noninterest Income	$ 0	$ 0	$ 0	$ 0