Financial Derivatives (Impact of Fair Value Hedge Accounting on the Carrying Value of Hedged Items) (Details) - Designated as Hedging Instrument - Fair Value Hedging - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Investment Securities
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	$ 2,785	$ 5,666
Cumulative fair value hedge adjustment included in the carrying value of hedged items	30	59
Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Value of the Hedged Items	25,797	28,616
Cumulative fair value hedge adjustment included in the carrying value of hedged items	1,611	548
Borrowed Funds Discontinued Relationships
Derivative Instruments, Gain (Loss) [Line Items]
Fair value hedge adjustments primarily related to discontinued borrowed funds hedge relationships, cumulative increase (decrease)	$ (100)	$ (300)

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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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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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