Derivatives and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative [Line Items]
Gross Fair Value of Derivative Asset Contracts Not Enforceable	$ 19,330		$ 19,330		$ 9,150
Gross Fair Value of Derivative Liability Contracts Not Enforceable	20,990		20,990		14,880
Net Gains / (Losses) on Derivative assets and liabilities	(323)	$ 237	1,610	$ 40
Net Realized Gains / (Losses) on Derivative assets and liabilities	(8)	75	142	89
Net Unrealized Gains / (Losses) on Derivative assets and liabilities	(315)	162	1,465	(49)
Maximum Payout/Notional Amount of Written Credit Derivative	558,186		558,186		522,569
Maximum Payout/Notional Amount of Purchased Credit Derivatives	607,730		607,730		581,760
Net purchased protection notional value of credit derivatives	49,540		49,540		59,190
Foreign Currency Denominated Debt Designated As Foreign Currency Hedge	3,700		3,700		3,050
Expected Reduction in Gross Credit Derivative Assets Due to Each Day Settlement					3,970
Expected Reduction in Gross Credit Derivative Liabilities Due to Each Day Settlement					$ 4,150
Net gain reclassified to earnings from accumulated other comprehensive income	61		61
Foreign Exchange Forward [Member] | Derivative Contracts Accounted for as Hedges [Member]
Derivative [Line Items]
Hedging Assets, Current	635		635
Net Investment Hedging [Member]
Derivative [Line Items]
Net gain reclassified to earnings from accumulated other comprehensive income	215		215
Net Investment Hedging [Member] | Non-US [Member]
Derivative [Line Items]
Net gain reclassified to earnings from accumulated other comprehensive income	(154)		(154)
Market making [Member]
Derivative [Line Items]
Net Gains / (Losses) on Derivative assets and liabilities	(289)	245	1,670	99
Other Principal Transactions [Member]
Derivative [Line Items]
Net Gains / (Losses) on Derivative assets and liabilities	$ (34)	$ (8)	$ (61)	$ (59)