Investment Securities Taxable and Nontaxable Interest Income by Investment Type (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Noninterest Income	$ 84	$ 49	$ 246	$ 143
Taxable [Member]
Noninterest Income	75	43	218	126
Nontaxable [Member]
Noninterest Income	9	6	28	17
Held-to-maturity Securities [Member]
Noninterest Income	5	5	17	16
Held-to-maturity Securities [Member] | Taxable [Member]
Noninterest Income	2	2	7	7
Held-to-maturity Securities [Member] | Nontaxable [Member]
Noninterest Income	3	3	10	9
Available-for-sale Securities [Member]
Noninterest Income	78	43	227	126
Available-for-sale Securities [Member] | Taxable [Member]
Noninterest Income	72	40	209	118
Available-for-sale Securities [Member] | Nontaxable [Member]
Noninterest Income	6	3	18	8
Trading Securities [Member]
Noninterest Income	1	1	2	1
Trading Securities [Member] | Taxable [Member]
Noninterest Income	1	1	2	1
Trading Securities [Member] | Nontaxable [Member]
Noninterest Income	$ 0	$ 0	$ 0	$ 0