Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 617	$ 1,686
Accruing Loans Contractually Past Due 90 Days or More	3	21
Nonaccrual Loans With No Allowance For Credit Losses	211	400
Residential mortgage loans carried at lower of cost or fair value of the collateral less cost to sell	86	375
Commercial loans:
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	379	544
Accruing Loans Contractually Past Due 90 Days or More	1	0
Nonaccrual Loans With No Allowance For Credit Losses	152	125
Commercial loans: | Real Estate, including Construction
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	140	44
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	20	31
Commercial loans: | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	134	163
Accruing Loans Contractually Past Due 90 Days or More	1	0
Nonaccrual Loans With No Allowance For Credit Losses	69	1
Commercial loans: | Global banking
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	105	337
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	63	93
Consumer loans:
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	238	1,142
Accruing Loans Contractually Past Due 90 Days or More	2	21
Nonaccrual Loans With No Allowance For Credit Losses	59	275
Consumer loans: | Loans held for sale | Exit of Mass Market Retail Banking Business and Remaining Retail Credit Card Portfolio
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	698
Accruing Loans Contractually Past Due 90 Days or More	21
Consumer loans: | Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	229	1,079
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	55	241
Consumer loans: | Home equity mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	9	63
Accruing Loans Contractually Past Due 90 Days or More	0	0
Nonaccrual Loans With No Allowance For Credit Losses	4	34
Consumer loans: | Credit cards
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Accruing Loans Contractually Past Due 90 Days or More	2	19
Nonaccrual Loans With No Allowance For Credit Losses	0	0
Consumer loans: | Other consumer
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	0	0
Accruing Loans Contractually Past Due 90 Days or More	0	2
Nonaccrual Loans With No Allowance For Credit Losses	0	0
Consumer loans: | Mortgage Loans Under Covid-19 Payment Deferral | Cares Act Election
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans	$ 12	$ 590