Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives	$ 276	$ 189	$ (22)		$ 1,738
Gain (loss) on instruments designated at fair value and related derivatives	15	(19)	15		(45)
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(274)	(213)	84	[1]	(1,816)	[1]
Credit risk component, total	(4)	(1)	(53)	[2],[3]	2	[3]
Total mark-to-market on financial instruments designated at fair value	(278)	(214)	31		(1,814)
Mark-to-market on related derivatives	283	184	(40)		1,739
Net realized gain on related long-term debt derivatives	10	11	24		30
Gain (loss) on instruments designated at fair value and related derivatives	15	(19)	15		(45)
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Loans [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	0	0	0	[1]	0	[1]
Credit risk component, assets	(4)	(1)	(53)	[2],[3]	2	[3]
Total mark-to-market on financial instruments designated at fair value	(4)	(1)	(53)		2
Mark-to-market on related derivatives	0	0	37		0
Net realized gain on related long-term debt derivatives	0	0	0		0
Gain (loss) on instruments designated at fair value and related derivatives	(4)	(1)	(16)		2
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Long-term debt [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	18	(115)	(114)	[1]	(284)	[1]
Credit risk component, liabilities	0	0	0	[2],[3]	0	[3]
Total mark-to-market on financial instruments designated at fair value	18	(115)	(114)		(284)
Mark-to-market on related derivatives	(24)	89	126		225
Net realized gain on related long-term debt derivatives	10	11	24		30
Gain (loss) on instruments designated at fair value and related derivatives	4	(15)	36		(29)
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Hybrid Instrument [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(292)	(98)	198	[1]	(1,532)	[1]
Credit risk component, liabilities	0	0	0	[2],[3]	0	[3]
Total mark-to-market on financial instruments designated at fair value	(292)	(98)	198		(1,532)
Mark-to-market on related derivatives	307	95	(203)		1,514
Net realized gain on related long-term debt derivatives	0	0	0		0
Gain (loss) on instruments designated at fair value and related derivatives	$ 15	$ (3)	$ (5)		$ (18)

[1] As it relates to hybrid instruments, interest rate and other components primarily includes interest rate, foreign exchange and equity contract risks.

[2] During the nine months ended September 30, 2020, the loss in the credit risk component for loans and loans held for sale was attributable to the widening of credit spreads associated with certain commercial loans held for sale which were impacted by the COVID-19 pandemic.

[3] The fair value movement on fair value option liabilities attributable to our own credit spread is recorded in other comprehensive income.