Derivative Instruments and Hedging Activities (Derivative gain (loss) recognized/reclassified) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion of Derivatives Gain/(Loss) Deferred in OCI	$ (4)
Amount of Gain/(Loss) Reclassified From OCI into Income	10	$ (1)	$ 13	$ (2)
Gains to be reclassified within the next 12 months into interest income			61
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Reclassified From OCI into Income	10	(1)	13	(2)
Derivatives Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion of Derivatives Gain/(Loss) Deferred in OCI	10	26	102	35
Excluded Components Deferred in OCI (Amortization Approach)	0	15	0	18
Amount of Gain/(Loss) Reclassified From OCI into Income	13	(2)	17	(4)
Hedge Ineffectiveness / OCI Reclass due to Missed Forecast	0	0	0	0
Interest on Fair Value Hedges	7	0	10	1
Derivatives Designated As Hedging Instruments [Member] \| Cash Flow Hedging [Member] \| Interest Rate Floor [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion of Derivatives Gain/(Loss) Deferred in OCI	0	2	0	2
Excluded Components Deferred in OCI (Amortization Approach)	0	15	0	18
Amount of Gain/(Loss) Reclassified From OCI into Income	3	(1)	6	(1)
Hedge Ineffectiveness / OCI Reclass due to Missed Forecast	0	0	0	0
Interest on Fair Value Hedges	0	0	0	0
Derivatives Designated As Hedging Instruments [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion of Derivatives Gain/(Loss) Deferred in OCI	10	24	102	33
Excluded Components Deferred in OCI (Amortization Approach)	0	0	0	0
Amount of Gain/(Loss) Reclassified From OCI into Income	10	(1)	11	(3)
Hedge Ineffectiveness / OCI Reclass due to Missed Forecast	0	0	0	0
Interest on Fair Value Hedges	0	0	0	0
Derivatives Designated As Hedging Instruments [Member] \| Fair Value Hedging [Member] \| Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion of Derivatives Gain/(Loss) Deferred in OCI	0	0	0	0
Excluded Components Deferred in OCI (Amortization Approach)	0	0	0	0
Amount of Gain/(Loss) Reclassified From OCI into Income	0	0	0	0
Hedge Ineffectiveness / OCI Reclass due to Missed Forecast	0	0	0	0
Interest on Fair Value Hedges	1	0	3	1
Derivatives Designated As Hedging Instruments [Member] \| Fair Value Hedging [Member] \| Terminated Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Effective Portion of Derivatives Gain/(Loss) Deferred in OCI	0	0	0	0
Excluded Components Deferred in OCI (Amortization Approach)	0	0	0	0
Amount of Gain/(Loss) Reclassified From OCI into Income	0	0	0	0
Hedge Ineffectiveness / OCI Reclass due to Missed Forecast	0	0	0	0
Interest on Fair Value Hedges	6	0	7	0
Derivatives Not Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest on Fair Value Hedges	2	6	17	12
Derivatives Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps For Customers [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest on Fair Value Hedges	34	86	346	132
Derivatives Not Designated As Hedging Instruments [Member] \| Offsetting Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest on Fair Value Hedges	(39)	(85)	(352)	(130)
Derivatives Not Designated As Hedging Instruments [Member] \| Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest on Fair Value Hedges	2	(1)	11	(1)
Derivatives Not Designated As Hedging Instruments [Member] \| Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest on Fair Value Hedges	$ 5	$ 6	$ 12	$ 11

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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The amount of net gain (loss) reclassified into earnings when interest rate cash flow hedge is discontinued because it is probable that the original forecasted transactions will not occur by the end of the original period or an additional two month time period.

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Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount, before tax, of adjustments from accumulated other comprehensive income (AOCI) for gain (loss) from increase (decrease) in value of excluded component of derivative designated and qualifying as hedge. Adjustments include, but are not limited to, reclassifications for sale and settlement, and amounts recognized under systematic and rational method.

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Derivative instrument noninterest income (expense)

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