Financial Derivatives (Impact of Fair Value Hedge Accounting on the Carrying Value of Hedged Items) (Details) - Fair value hedges - Designated as Hedging Instruments under GAAP - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Investment Securities
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	$ 2,905	$ 2,785
Cumulative Fair Value Hedge Adjustment included in the Carrying Value of Hedged Items	25	30
Borrowed Funds
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	25,924	25,797
Cumulative Fair Value Hedge Adjustment included in the Carrying Value of Hedged Items	906	1,611
Borrowed Funds Discontinued Relationships
Derivative Instruments, Gain (Loss) [Line Items]
Cumulative fair value hedge adjustment included in carrying value of hedged items	$ (100)	$ (100)

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No definition available.

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- Definition

Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk, remaining after discontinued hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109999712-113959

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- Definition

Amount of asset hedged in fair value hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109999712-113959

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- Definition

Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109999712-113959

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