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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
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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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- Definition 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 + Details
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