Investment Securities Taxable and Nontaxable Interest Income by Investment Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Noninterest Income	$ 96	$ 86
Taxable [Member]
Noninterest Income	85	75
Nontaxable [Member]
Noninterest Income	11	11
Held-to-maturity Securities [Member]
Noninterest Income	6	6
Held-to-maturity Securities [Member] | Taxable [Member]
Noninterest Income	2	2
Held-to-maturity Securities [Member] | Nontaxable [Member]
Noninterest Income	4	4
Available-for-sale Securities [Member]
Noninterest Income	89	79
Available-for-sale Securities [Member] | Taxable [Member]
Noninterest Income	83	73
Available-for-sale Securities [Member] | Nontaxable [Member]
Noninterest Income	6	6
Other Trading [Member]
Noninterest Income	1	1
Other Trading [Member] | Taxable [Member]
Noninterest Income	0	0
Other Trading [Member] | Nontaxable [Member]
Noninterest Income	$ 1	$ 1