Investment Securities Taxable and Nontaxable Interest Income by Investment Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Noninterest Income	$ 78	$ 47
Taxable [Member]
Noninterest Income	69	42
Nontaxable [Member]
Noninterest Income	9	5
Held-to-maturity Securities [Member]
Noninterest Income	7	5
Held-to-maturity Securities [Member] | Taxable [Member]
Noninterest Income	3	2
Held-to-maturity Securities [Member] | Nontaxable [Member]
Noninterest Income	4	3
Available-for-sale Securities [Member]
Noninterest Income	71	42
Available-for-sale Securities [Member] | Taxable [Member]
Noninterest Income	66	40
Available-for-sale Securities [Member] | Nontaxable [Member]
Noninterest Income	$ 5	$ 2