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Derivative Instruments and Hedging Activities - Gains Losses on Freestanding Derivatives (Details) - Other non-interest income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	$ 43	$ 52	$ 60
Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	55	78	48
Interest rate contracts | Customer accommodation
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	15	48	25
Interest rate contracts | Other interest rate exposures
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	(8)	(16)	33
Commodity contracts | Customer accommodation
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	32	17	16
Foreign exchange contracts | Customer accommodation
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	8	13	7
Other contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on derivatives not designated as accounting hedges	$ (4)	$ (10)	$ (21)

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959

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