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, 2020	Dec. 31, 2019
Investment Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	$ 3,237	$ 5,666
Cumulative Fair Value Hedge Adjustment included in the Carrying Value of Hedged Items	59	59
Borrowed Funds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	28,326	28,616
Cumulative Fair Value Hedge Adjustment included in the Carrying Value of Hedged Items	1,850	548
Borrowed Funds Discontinued Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cumulative Fair Value Hedge Adjustment included in Carrying Value of Hedged Items	$ (200)	$ (300)