Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives		$ 367	$ (1,354)
Gain (loss) on instruments designated at fair value and related derivatives		18	(22)
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	[1]	(352)	1,445
Credit risk component, total	[2]	1	(54)	[3]
Total mark-to-market on financial instruments designated at fair value		(351)	1,391
Mark-to-market on related derivatives		360	(1,419)
Net realized gain on related long-term debt derivatives		9	6
Gain (loss) on instruments designated at fair value and related derivatives		18	(22)
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	[1]	0	0
Credit risk component, assets	[2]	1	(54)	[3]
Total mark-to-market on financial instruments designated at fair value		1	(54)
Mark-to-market on related derivatives		0	37
Net realized gain on related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		1	(17)
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	[1]	100	(134)
Credit risk component, liabilities	[2]	0	0	[3]
Total mark-to-market on financial instruments designated at fair value		100	(134)
Mark-to-market on related derivatives		(108)	150
Net realized gain on related long-term debt derivatives		9	6
Gain (loss) on instruments designated at fair value and related derivatives		1	22
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	[1]	(452)	1,579
Credit risk component, liabilities	[2]	0	0	[3]
Total mark-to-market on financial instruments designated at fair value		(452)	1,579
Mark-to-market on related derivatives		468	(1,606)
Net realized gain on related long-term debt derivatives		0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ 16	$ (27)

[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.

[3] During the three months ended March 31, 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.