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
	Mar. 31, 2022		Mar. 31, 2021
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	$ 447	[1]	$ 1,015
Provision charged (credited) to income	31		(145)
Charge offs	(19)		(25)
Recoveries	8		8
Net (charge offs) recoveries	(11)		(17)
Allowance for credit losses - end of period	467	[1]	853
Commercial loans: | Real Estate, including Construction
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	73		145
Provision charged (credited) to income	49		(25)
Charge offs	0		0
Recoveries	0		0
Net (charge offs) recoveries	0		0
Allowance for credit losses - end of period	122		120
Commercial loans: | Business and corporate banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	243		375
Provision charged (credited) to income	(40)		(53)
Charge offs	(8)		(2)
Recoveries	2		1
Net (charge offs) recoveries	(6)		(1)
Allowance for credit losses - end of period	197		321
Commercial loans: | Global banking
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	100		287
Provision charged (credited) to income	29		(65)
Charge offs	(9)		0
Recoveries	0		0
Net (charge offs) recoveries	(9)		0
Allowance for credit losses - end of period	120		222
Commercial loans: | Other commercial:
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	4		7
Provision charged (credited) to income	(2)		0
Charge offs	0		0
Recoveries	0		0
Net (charge offs) recoveries	0		0
Allowance for credit losses - end of period	2		7
Consumer loans: | Residential Mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	8		(9)
Provision charged (credited) to income	(4)		(2)
Charge offs	(1)		(1)
Recoveries	2		3
Net (charge offs) recoveries	1		2
Allowance for credit losses - end of period	5		(9)
Consumer loans: | Home equity mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	5		22
Provision charged (credited) to income	0		(3)
Charge offs	(1)		0
Recoveries	2		2
Net (charge offs) recoveries	1		2
Allowance for credit losses - end of period	6		21
Consumer loans: | Credit cards
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	14		161
Provision charged (credited) to income	(1)		(1)
Charge offs	0		(18)
Recoveries	2		2
Net (charge offs) recoveries	2		(16)
Allowance for credit losses - end of period	15		144
Consumer loans: | Other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses - beginning of period	0		27
Provision charged (credited) to income	0		4
Charge offs	0		(4)
Recoveries	0		0
Net (charge offs) recoveries	0		(4)
Allowance for credit losses - end of period	$ 0		$ 27

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at March 31, 2022 and December 31, 2021. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 17, "Variable Interest Entities," for additional information. March 31, 2022December 31, 2021(in millions)AssetsLoans$128 $46 Other assets51 55 Total assets$179 $101 LiabilitiesInterest, taxes and other liabilities$31 $9 Total liabilities$31 $9