Derivative instruments - Revenue from Foreign Exchange and Other Trading (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Foreign exchange revenue	$ 185	$ 184	$ 149	$ 600	$ 587
Other trading revenue (loss)	$ 20	$ (1)	$ (14)	$ 12	$ 44

Amount of gain (loss) resulting from the difference between the acquisition price and the selling price or fair value of trading assets and trading liabilities, conducted separately from customer trading activities. Includes, but is not limited to, changes in fair value of trading assets and trading liabilities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration