Derivative Instruments and Hedging Activities (Derivative Gain (Loss) Recognized/Reclassified) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivatives gain/(loss) deferred in OCI	$ (21)
Amount of gain/(loss) reclassified from OCI into income	12	$ 11	$ 35	$ 24
Gains to be reclassified within the next 12 months into interest income			42
Derivatives designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivatives gain/(loss) deferred in OCI	4	(1)	(5)	101
Excluded components deferred in OCI (amortization approach)	0	0	0	0
Amount of gain/(loss) reclassified from OCI into income	16	16	46	32
Interest on fair value hedges	4	4	13	14
Hedge ineffectiveness/OCI reclass due to missed forecast	0	0	0	0
Derivatives designated as hedges \| Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Terminated or redesignated, unamortized basis adjustments	7		7
Derivatives designated as hedges \| Cash Flow Hedging \| Purchased interest rate floors
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	3	3	8	8
Interest on fair value hedges	0	0	0	0
Hedge ineffectiveness/OCI reclass due to missed forecast	0	0	0	0
Derivatives designated as hedges \| Cash Flow Hedging \| Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivatives gain/(loss) deferred in OCI	4	(1)	(5)	101
Excluded components deferred in OCI (amortization approach)	0	0	0	0
Amount of gain/(loss) reclassified from OCI into income	13	13	38	24
Interest on fair value hedges	0	0	0	0
Hedge ineffectiveness/OCI reclass due to missed forecast	0	0	0	0
Derivatives designated as hedges \| Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Terminated or redesignated, unamortized basis adjustments	2		2
Derivatives designated as hedges \| Fair Value Hedging \| Receive-fixed interest rate swaps
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
Interest on fair value hedges	2	1	6	4
Hedge ineffectiveness/OCI reclass due to missed forecast	0	0	0	0
Derivatives designated as hedges \| Fair Value Hedging \| Basis amortization on terminated hedges
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
Interest on fair value hedges	3	3	9	10
Hedge ineffectiveness/OCI reclass due to missed forecast	0	0	0	0
Derivatives designated as hedges \| Fair Value Hedging \| Pay-fixed interest rate swaps
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
Interest on fair value hedges	(1)	0	(2)	0
Hedge ineffectiveness/OCI reclass due to missed forecast	0	0	0	0
Derivatives designated as hedges \| Fair Value Hedging \| Basis amortization on terminated hedges
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
Interest on fair value hedges	0	0	0	0
Hedge ineffectiveness/OCI reclass due to missed forecast	$ 0	$ 0	$ 0	$ 0

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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