Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2022		Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2022		Sep. 30, 2021
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	$ 534		$ 547		$ 447	[1]	$ 1,015
Provision charged (credited) to income	16		(64)		110		(410)
Charge-offs	(2)		(16)		(22)		(155)
Recoveries	3		8		16		25
Net (charge-offs) recoveries	1		(8)		(6)		(130)
Allowance for credit losses - end of period	551	[1]	475	$ 547	551	[1]	475
Exit of Mass Market Retail Banking Business
Allowance for Loan and Lease Losses [Roll Forward]
Reduction to the provision for credit losses				101
Commercial loans | Real Estate, including Construction
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	162		117		73		145
Provision charged (credited) to income	27		(2)		116		(30)
Charge-offs	0		0		0		0
Recoveries	0		0		0		0
Net (charge-offs) recoveries	0		0		0		0
Allowance for credit losses - end of period	189		115	117	189		115
Reduction to the provision for credit losses			24
Commercial loans | Business and corporate banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	218		284		243		375
Provision charged (credited) to income	(11)		(38)		(29)		(115)
Charge-offs	(2)		(13)		(11)		(29)
Recoveries	1		1		3		3
Net (charge-offs) recoveries	(1)		(12)		(8)		(26)
Allowance for credit losses - end of period	206		234	284	206		234
Commercial loans | Global banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	118		131		100		287
Provision charged (credited) to income	2		(9)		29		(153)
Charge-offs	0		0		(9)		(12)
Recoveries	0		0		0		0
Net (charge-offs) recoveries	0		0		(9)		(12)
Allowance for credit losses - end of period	120		122	131	120		122
Commercial loans | Other commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	1		6		4		7
Provision charged (credited) to income	0		(2)		(3)		(3)
Charge-offs	0		0		0		0
Recoveries	0		0		0		0
Net (charge-offs) recoveries	0		0		0		0
Allowance for credit losses - end of period	1		4	6	1		4
Consumer loans | Exit of Mass Market Retail Banking Business
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs				(56)
Reduction to the provision for credit losses				100
Consumer loans | Residential mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	6		(6)		8		(9)
Provision charged (credited) to income	2		(9)		(3)		(3)
Charge-offs	0		0		(1)		(10)
Recoveries	1		4		5		11
Net (charge-offs) recoveries	1		4		4		1
Allowance for credit losses - end of period	9		(11)	(6)	9		(11)
Consumer loans | Home equity mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	7		15		5		22
Provision charged (credited) to income	(2)		(2)		(1)		(10)
Charge-offs	0		(3)		(1)		(5)
Recoveries	1		1		3		4
Net (charge-offs) recoveries	1		(2)		2		(1)
Allowance for credit losses - end of period	6		11	15	6		11
Consumer loans | Credit cards
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	22		0		14		161
Provision charged (credited) to income	(2)		(1)		2		(78)
Charge-offs	0		0		0		(88)
Recoveries	0		1		4		5
Net (charge-offs) recoveries	0		1		4		(83)
Allowance for credit losses - end of period	20		0	0	20		0
Consumer loans | Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	0		0		0		27
Provision charged (credited) to income	0		(1)		(1)		(18)
Charge-offs	0		0		0		(11)
Recoveries	0		1		1		2
Net (charge-offs) recoveries	0		1		1		(9)
Allowance for credit losses - end of period	$ 0		$ 0	$ 0	$ 0		$ 0

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at September 30, 2022 and December 31, 2021. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 17, "Variable Interest Entities," for additional information. September 30, 2022December 31, 2021(in millions)AssetsLoans$127 $46 Other assets44 55 Total assets$171 $101 LiabilitiesInterest, taxes and other liabilities$26 $9 Total liabilities$26 $9