Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 41	$ 247	$ 397
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	6	200	323
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	6	40	323
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	0	160	0
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 35	$ 47	$ 74
Weighted average rate of reduction	1.93%	1.91%	1.48%
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 26	$ 34	$ 62
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	5	9	8
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 4	$ 4	$ 4