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			6 Months Ended
	Jun. 30, 2022		Jun. 30, 2021	Jun. 30, 2022		Jun. 30, 2021
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	$ 467		$ 853	$ 447	[1]	$ 1,015
Provision charged (credited) to income	63		(201)	94		(346)
Charge-offs	(1)		(114)	(20)		(139)
Recoveries	5		9	13		17
Net (charge-offs) recoveries	4		(105)	(7)		(122)
Allowance for credit losses - end of period	534	[1]	547	534	[1]	547
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	122		120	73		145
Provision charged (credited) to income	40		(3)	89		(28)
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	162		117	162		117
Commercial loans | Business and corporate banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	197		321	243		375
Provision charged (credited) to income	22		(24)	(18)		(77)
Charge-offs	(1)		(14)	(9)		(16)
Recoveries	0		1	2		2
Net (charge-offs) recoveries	(1)		(13)	(7)		(14)
Allowance for credit losses - end of period	218		284	218		284
Commercial loans | Global banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	120		222	100		287
Provision charged (credited) to income	(2)		(79)	27		(144)
Charge-offs	0		(12)	(9)		(12)
Recoveries	0		0	0		0
Net (charge-offs) recoveries	0		(12)	(9)		(12)
Allowance for credit losses - end of period	118		131	118		131
Commercial loans | Other commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	2		7	4		7
Provision charged (credited) to income	(1)		(1)	(3)		(1)
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		6	1		6
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	5		(9)	8		(9)
Provision charged (credited) to income	(1)		8	(5)		6
Charge-offs	0		(9)	(1)		(10)
Recoveries	2		4	4		7
Net (charge-offs) recoveries	2		(5)	3		(3)
Allowance for credit losses - end of period	6		(6)	6		(6)
Consumer loans | Home equity mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	6		21	5		22
Provision charged (credited) to income	1		(5)	1		(8)
Charge-offs	0		(2)	(1)		(2)
Recoveries	0		1	2		3
Net (charge-offs) recoveries	0		(1)	1		1
Allowance for credit losses - end of period	7		15	7		15
Consumer loans | Credit cards
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	15		144	14		161
Provision charged (credited) to income	5		(76)	4		(77)
Charge-offs	0		(70)	0		(88)
Recoveries	2		2	4		4
Net (charge-offs) recoveries	2		(68)	4		(84)
Allowance for credit losses - end of period	22		0	22		0
Consumer loans | Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	0		27	0		27
Provision charged (credited) to income	(1)		(21)	(1)		(17)
Charge-offs	0		(7)	0		(11)
Recoveries	1		1	1		1
Net (charge-offs) recoveries	1		(6)	1		(10)
Allowance for credit losses - end of period	$ 0		$ 0	$ 0		$ 0

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at June 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. June 30, 2022December 31, 2021(in millions)AssetsLoans$118 $46 Other assets46 55 Total assets$164 $101 LiabilitiesInterest, taxes and other liabilities$28 $9 Total liabilities$28 $9