Loans - Summary of Past Due Status of Loans (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans	[1]	$ 55,864	$ 62,088
Commercial loans:
Financing Receivable, Past Due [Line Items]
Loans		39,796	41,599
Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Loans		8,234	10,464
Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans		13,958	13,479
Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Loans		11,109	13,519
Commercial loans: | Other commercial
Financing Receivable, Past Due [Line Items]
Loans		6,495	4,137
Consumer loans:
Financing Receivable, Past Due [Line Items]
Loans		16,068	20,489
Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans		15,469	18,377
Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans		325	727
Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Loans		204	1,066
Consumer loans: | Other consumer
Financing Receivable, Past Due [Line Items]
Loans		70	319
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans		453	1,141
Financial Asset, Past Due | Commercial loans:
Financing Receivable, Past Due [Line Items]
Loans		241	307
Financial Asset, Past Due | Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Loans		38	78
Financial Asset, Past Due | Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans		129	145
Financial Asset, Past Due | Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Loans		27	60
Financial Asset, Past Due | Commercial loans: | Other commercial
Financing Receivable, Past Due [Line Items]
Loans		47	24
Financial Asset, Past Due | Consumer loans:
Financing Receivable, Past Due [Line Items]
Loans		212	834
Financial Asset, Past Due | Consumer loans: | Exit of Mass Market Retail Banking Business and Remaining Retail Credit Card Portfolio | Loans held for sale
Financing Receivable, Past Due [Line Items]
Loans		419
Financial Asset, Past Due | Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans		201	746
Financial Asset, Past Due | Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans		3	33
Financial Asset, Past Due | Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Loans		7	42
Financial Asset, Past Due | Consumer loans: | Other consumer
Financing Receivable, Past Due [Line Items]
Loans		1	13
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Loans		343	704
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial loans:
Financing Receivable, Past Due [Line Items]
Loans		197	228
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Loans		38	78
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans		112	126
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Loans		0	0
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial loans: | Other commercial
Financing Receivable, Past Due [Line Items]
Loans		47	24
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer loans:
Financing Receivable, Past Due [Line Items]
Loans		146	476
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans		138	435
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans		2	11
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Loans		5	23
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer loans: | Other consumer
Financing Receivable, Past Due [Line Items]
Loans		1	7
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Loans		110	437
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial loans:
Financing Receivable, Past Due [Line Items]
Loans		44	79
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Loans		0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans		17	19
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Loans		27	60
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial loans: | Other commercial
Financing Receivable, Past Due [Line Items]
Loans		0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer loans:
Financing Receivable, Past Due [Line Items]
Loans		66	358
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans		63	311
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans		1	22
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Loans		2	19
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer loans: | Other consumer
Financing Receivable, Past Due [Line Items]
Loans		0	6
Financial Asset, Not Past Due [Member]
Financing Receivable, Past Due [Line Items]
Loans		55,411	60,947
Financial Asset, Not Past Due [Member] | Commercial loans:
Financing Receivable, Past Due [Line Items]
Loans		39,555	41,292
Financial Asset, Not Past Due [Member] | Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Loans		8,196	10,386
Financial Asset, Not Past Due [Member] | Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Loans		13,829	13,334
Financial Asset, Not Past Due [Member] | Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Loans		11,082	13,459
Financial Asset, Not Past Due [Member] | Commercial loans: | Other commercial
Financing Receivable, Past Due [Line Items]
Loans		6,448	4,113
Financial Asset, Not Past Due [Member] | Consumer loans:
Financing Receivable, Past Due [Line Items]
Loans		15,856	19,655
Financial Asset, Not Past Due [Member] | Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans		15,268	17,631
Financial Asset, Not Past Due [Member] | Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Loans		322	694
Financial Asset, Not Past Due [Member] | Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Loans		197	1,024
Financial Asset, Not Past Due [Member] | Consumer loans: | Other consumer
Financing Receivable, Past Due [Line Items]
Loans		$ 69	$ 306

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at December 31, 2021 and 2020. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 27, "Variable Interest Entities," for additional information. At December 31,20212020(in millions)AssetsLoans$46 $10 Other assets55 79 Total assets$101 $89 LiabilitiesInterest, taxes and other liabilities$9 $10 Total liabilities$9 $10