Investment Securities (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Securities	Dec. 31, 2016 USD ($) Securities	Dec. 31, 2015 USD ($)
Investment [Line Items]
Interest on securities	$ 326	$ 204	$ 124
Number of HTM investment securities in an unrealized loss position | Securities	667	642
Number of AFS investment securities in an unrealized loss position | Securities	2,262	2,398
Carrying value of pledged securities	$ 2,100	$ 1,400
Available-for-sale Securities, Amortized Cost Basis	15,313	$ 13,521
Private equity investments prohibited by Volker rule	3
Commitments for Private Equity and Other Noninterest-bearing Investments	31
Private Equity Investments	141
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule	$ 4