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, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives	$ (73)	$ 276	$ 729		$ (22)
Gain (loss) on instruments designated at fair value and related derivatives	8	15	33		15
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	78	(274)	(716)	[1]	84	[1]
Credit risk component, total	0	(4)	1	[2]	(53)	[2],[3]
Total mark-to-market on financial instruments designated at fair value	78	(278)	(715)		31
Mark-to-market on related derivatives	(80)	283	719		(40)
Net realized gain on related long-term debt derivatives	10	10	29		24
Gain (loss) on instruments designated at fair value and related derivatives	8	15	33		15
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	0	(4)	1	[2]	(53)	[2],[3]
Total mark-to-market on financial instruments designated at fair value	0	(4)	1		(53)
Mark-to-market on related derivatives	0	0	0		37
Net realized gain on related long-term debt derivatives	0	0	0		0
Gain (loss) on instruments designated at fair value and related derivatives	0	(4)	1		(16)
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	16	18	75	[1]	(114)	[1]
Credit risk component, liabilities	0	0	0	[2]	0	[2],[3]
Total mark-to-market on financial instruments designated at fair value	16	18	75		(114)
Mark-to-market on related derivatives	(19)	(24)	(85)		126
Net realized gain on related long-term debt derivatives	10	10	29		24
Gain (loss) on instruments designated at fair value and related derivatives	7	4	19		36
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	62	(292)	(791)	[1]	198	[1]
Credit risk component, liabilities	0	0	0	[2]	0	[2],[3]
Total mark-to-market on financial instruments designated at fair value	62	(292)	(791)		198
Mark-to-market on related derivatives	(61)	307	804		(203)
Net realized gain on related long-term debt derivatives	0	0	0		0
Gain (loss) on instruments designated at fair value and related derivatives	$ 1	$ 15	$ 13		$ (5)

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

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

[3] 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.