Derivative instruments - Impact of Derivative Instruments on the Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Asset derivatives fair value
Total derivatives fair value	$ 10,278	$ 12,191
Effect of master netting agreements	(5,875)	(8,346)
Fair value after effect of master netting agreements	4,403	3,845
Liability derivatives fair value
Total derivatives fair value	9,649	12,650
Effect of master netting agreements	(6,529)	(7,845)
Fair value after effect of master netting agreements	3,120	4,805
Derivative asset, collateral, obligation to return cash, offset	1,060	1,552
Derivative liability, collateral, right to reclaim cash, offset	1,714	1,051
Interest rate contracts
Asset derivatives fair value
Effect of master netting agreements	(1,456)	(1,952)
Liability derivatives fair value
Effect of master netting agreements	(1,844)	(2,348)
Foreign exchange contracts
Asset derivatives fair value
Effect of master netting agreements	(4,251)	(6,392)
Liability derivatives fair value
Effect of master netting agreements	(4,685)	(5,484)
Equity contracts
Asset derivatives fair value
Effect of master netting agreements	(168)	(2)
Liability derivatives fair value
Effect of master netting agreements	0	(13)
Designated as hedging
Asset derivatives fair value
Total derivatives fair value	238	19
Liability derivatives fair value
Total derivatives fair value	428	1,107
Designated as hedging | Interest rate contracts
Notional value
Notional amount of hedge	45,771	31,360
Asset derivatives fair value
Total derivatives fair value	0	0
Liability derivatives fair value
Total derivatives fair value	421	666
Designated as hedging | Foreign exchange contracts
Notional value
Notional amount of hedge	8,749	8,706
Asset derivatives fair value
Total derivatives fair value	238	19
Liability derivatives fair value
Total derivatives fair value	7	441
Not designated as hedging
Asset derivatives fair value
Total derivatives fair value	10,040	12,172
Liability derivatives fair value
Total derivatives fair value	9,221	11,543
Not designated as hedging | Interest rate contracts
Notional value
Notional amount of hedge	195,065	198,865
Asset derivatives fair value
Total derivatives fair value	3,424	4,482
Liability derivatives fair value
Total derivatives fair value	2,989	3,880
Not designated as hedging | Foreign exchange contracts
Notional value
Notional amount of hedge	925,721	813,003
Asset derivatives fair value
Total derivatives fair value	6,351	7,688
Liability derivatives fair value
Total derivatives fair value	6,218	7,622
Not designated as hedging | Equity contracts
Notional value
Notional amount of hedge	8,214	5,142
Asset derivatives fair value
Total derivatives fair value	265	2
Liability derivatives fair value
Total derivatives fair value	9	37
Not designated as hedging | Credit contracts
Notional value
Notional amount of hedge	190	165
Asset derivatives fair value
Total derivatives fair value	0	0
Liability derivatives fair value
Total derivatives fair value	$ 5	$ 4