Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Impaired [Line Items]
Total	$ 144	$ 75
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	114	39
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	114	26
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	0	13
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	30	36
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	27	35
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Total	2	0
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 1	$ 1