Derivative instruments - Notional Amount of Derivative Contracts (Details) - USD ($) $ in Billions	Sep. 30, 2015	Dec. 31, 2014
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	$ 52,018	$ 63,662
Interest rate contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	37,294	48,085
Interest rate swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	24,058	29,734
Interest rate futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	5,377	10,189
Interest rate options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	3,689	3,903
Interest rate options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	4,170	4,259
Credit derivatives
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	3,503	4,249
Foreign exchange contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	9,527	9,585
Foreign exchange cross-currency swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	3,052	3,346
Foreign exchange spot, futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	4,976	4,669
Foreign exchange options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	759	790
Foreign exchange options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	740	780
Equity contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	1,117	1,063
Equity swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	227	206
Equity futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	45	50
Equity options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	457	432
Equity options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	388	375
Commodity contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	577	680
Commodity swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	103	126
Commodity spot, futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	132	193
Commodity options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	172	181
Commodity options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	$ 170	$ 180