Financial Derivatives (Gains (Losses) on Derivatives and Related Hedged Items - Fair Value Hedges) (Details) - Fair Value Hedging - Designated as Hedging Instrument - Interest Rate Contract - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives Recognized in Income	$ (236)	$ (190)	$ (108)
Gain (Loss) on Related Hedged Items Recognized in Income	218	158	67
Us Treasury And Government And Other Debt Securities | Investment Securities Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives Recognized in Income	48	142
Gain (Loss) on Related Hedged Items Recognized in Income	(50)	(141)
Subordinated debt and Bank notes and senior debt | Borrowed Funds Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives Recognized in Income	(284)	(332)	(108)
Gain (Loss) on Related Hedged Items Recognized in Income	$ 268	$ 299	$ 67