Investment Securities (Narrative) (Details) $ in Millions	Sep. 30, 2017 USD ($) Securities	Dec. 31, 2016 USD ($) Securities
Investment [Line Items]
Private equity investments prohibited by Volker rule	$ 4
Number of HTM investment securities in an unrealized loss position | Securities	360	642
Number of AFS investment securities in an unrealized loss position | Securities	1,446	2,398
Carrying value of pledged securities	$ 2,300	$ 1,400
Private Equity Investments	138
Commitments for Private Equity and Other Noninterest-bearing Investments	27
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule	4
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized cost	$ 746	$ 868