Financial Derivatives (Gains (Losses) on Derivatives and Related Hedged Items - Fair Value Hedges) (Details) - Fair Value Hedging [Member] - Designated as Hedging Instrument [Member] - Interest Rate Contracts [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives Recognized in Income	$ (47)	$ (181)	$ (87)	$ 172
Gain (Loss) on Related Hedged Items Recognized in Income	42	178	65	(208)
Us Treasury And Government And Other Debt Securities [Member] | Investment Securities Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives Recognized in Income	9	51	(3)	(158)
Gain (Loss) on Related Hedged Items Recognized in Income	(8)	(53)	4	161
Subordinated debt and Bank notes and senior debt [Member] | Borrowed Funds Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivatives Recognized in Income	(56)	(232)	(84)	330
Gain (Loss) on Related Hedged Items Recognized in Income	$ 50	$ 231	$ 61	$ (369)