Investment Securities (Narrative) (Details) $ in Millions		3 Months Ended	12 Months Ended	15 Months Ended
	Mar. 31, 2017 USD ($) Securities yr	Mar. 31, 2017 USD ($) Securities	Dec. 31, 2016 USD ($) Securities	Mar. 31, 2017 USD ($) Securities
Investment [Line Items]
Private equity investments prohibited by Volker rule	$ 5	$ 5		$ 5
Number of HTM investment securities in an unrealized loss position | Securities	453	453	642	453
Number of AFS investment securities in an unrealized loss position | Securities	2,121	2,121	2,398	2,121
Carrying value of pledged securities	$ 2,100	$ 2,100	$ 1,400	$ 2,100
Private Equity Investments	143	143		143
Private Equity Investments Sold Prohibited by Volcker Rule		1	10	11
Commitments for Private Equity and Other Noninterest-bearing Investments	24	24		24
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule	$ 3	3		3
Small Business Administration Loan-Backed Securities [Member] | Minimum [Member]
Investment [Line Items]
Investment term of maturity | yr	5
Small Business Administration Loan-Backed Securities [Member] | Maximum [Member]
Investment [Line Items]
Investment term of maturity | yr	25
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost	$ 815	$ 815	$ 868	$ 815