Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 11	$ 58
Commercial loans:
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	2	41
Commercial loans: | Business and corporate banking
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	2	26
Commercial loans: | Global banking
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	0	15
Consumer loans:
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	9	17
Consumer loans: | Residential mortgages
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	7	16
Consumer loans: | Credit cards
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 2	$ 1