Financial Derivatives (Impact of Fair Value Hedge Accounting on the Carrying Value of Hedged Items) (Details) - Fair Value Hedging [Member] - Designated as Hedging Instruments under GAAP [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investment Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	$ 6,787	$ 6,216
Cumulative Fair Value Hedge Adjustment included in the Carrying Value of Hedged Items	132	(103)
Borrowed Funds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	26,873	27,121
Cumulative Fair Value Hedge Adjustment included in the Carrying Value of Hedged Items	807	(260)
Borrowed Funds Discontinued Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cumulative Fair Value Hedge Adjustment included in Carrying Value of Hedged Items	$ (300)	$ (500)