Derivatives and Hedging Activities - Fair Values, Volume of Activity and Gain (Loss) Information Related to Derivative Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ 99,869	$ 88,288
Derivative Assets, Netting adjustments	(390)	(431)
Derivative Assets, net	615	782
Derivative Liabilities, Netting adjustments	(557)	(384)
Derivative Liabilities, net	151	539
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	25,779	24,519
Derivative Assets	87	195
Derivative Liabilities	44	98
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	74,090	63,769
Derivative Assets	925	1,039
Derivative Liabilities	745	922
Interest Rate [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	25,489	24,237
Derivative Assets	87	189
Derivative Liabilities	29	94
Interest Rate [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	60,887	55,315
Derivative Assets	644	741
Derivative Liabilities	469	643
Foreign Exchange [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	290	282
Derivative Assets	0	6
Derivative Liabilities	15	4
Foreign Exchange [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	8,664	6,230
Derivative Assets	129	117
Derivative Liabilities	122	109
Commodity [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	1,696	1,474
Derivative Assets	144	176
Derivative Liabilities	135	165
Credit [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	484	360
Derivative Assets	1	1
Derivative Liabilities	6	4
Other [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	2,359	390
Derivative Assets	7	4
Derivative Liabilities	13	1
Net Derivatives [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	99,869	88,288
Derivative Assets, net	622	803
Derivative Liabilities, net	232	636
Counterparty And Cash Collateral Netting [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	0	0
Derivative Assets, net	(7)	(21)
Derivative Liabilities, net	$ (81)	$ (97)