Derivative Instruments - Notional Amount of Derivative Contracts (Details) - USD ($) $ in Billions	Sep. 30, 2018	Dec. 31, 2017
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	$ 58,980	$ 48,386
Interest rate contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	42,513	33,510
Swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	25,236	21,043
Futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	7,326	4,904
Options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	4,718	3,576
Options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	5,233	3,987
Credit derivatives
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	1,603	1,522
Foreign exchange contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	12,622	11,438
Cross-currency swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	3,893	3,953
Spot, futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	6,812	5,923
Options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	961	786
Options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	956	776
Equity contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	1,647	1,441
Swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	402	367
Futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	106	90
Options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	596	531
Options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	543	453
Commodity contracts
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	595	475
Swaps
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	140	116
Spot, futures and forwards
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	164	168
Options | Written options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	157	98
Options | Purchased options
Notional amount of derivative contracts outstanding [Abstract]
Derivative notional amounts	$ 134	$ 93