Derivative instruments - Revenue from Foreign Exchange and Other Trading (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Foreign exchange	$ 174	$ 253	$ 150	$ 427	$ 310
Other trading revenue	(8)	66	16	58	26
Total foreign exchange and other trading revenue	$ 166	$ 319	$ 166	$ 485	$ 336

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