Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Mark-to-market on related derivatives		$ 824		$ 2,082	$ (1,131)
Gain (loss) on instruments designated at fair value and related derivatives		34		(13)	19
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]	(774)		(2,186)	1,135
Credit risk component, total	[3]	(49)	[2]	3	(4)
Total mark-to-market on financial instruments designated at fair value		(823)		(2,183)	1,131
Mark-to-market on related derivatives		824		2,131	(1,157)
Net realized gain on related long-term debt derivatives		33		39	45
Gain (loss) on instruments designated at fair value and related derivatives		34		(13)	19
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	0
Credit risk component, assets	[3]	(49)	[2]	3	(4)
Total mark-to-market on financial instruments designated at fair value		(49)		3	(4)
Mark-to-market on related derivatives		37		0	0
Net realized gain on related long-term debt derivatives		0		0	0
Gain (loss) on instruments designated at fair value and related derivatives		(12)		3	(4)
Gain (Loss) on Instruments Designated at Fair Value and Related Derivatives [Member] | Securities sold under repurchase agreements [Member]
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	[1]				1
Credit risk component, assets	[3]				0
Total mark-to-market on financial instruments designated at fair value					1
Mark-to-market on related derivatives					0
Net realized gain on related long-term debt derivatives					0
Gain (loss) on instruments designated at fair value and related derivatives					1
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]	(79)		(200)	99
Credit risk component, liabilities	[3]	0	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		(79)		(200)	99
Mark-to-market on related derivatives		88		148	(95)
Net realized gain on related long-term debt derivatives		33		39	45
Gain (loss) on instruments designated at fair value and related derivatives		42		(13)	49
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]	(695)		(1,986)	1,035
Credit risk component, liabilities	[3]	0	[2]	0	0
Total mark-to-market on financial instruments designated at fair value		(695)		(1,986)	1,035
Mark-to-market on related derivatives		699		1,983	(1,062)
Net realized gain on related long-term debt derivatives		0		0	0
Gain (loss) on instruments designated at fair value and related derivatives		$ 4		$ (3)	$ (27)

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

[2] During 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.