Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 15	$ 136	$ 369	$ 276
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	0	87	304	154
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	0	0	0	4
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	0	87	304	137
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	0	0	13
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	15	49	65	122
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	12	47	55	117
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	2	1	7	2
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Loans which were modified and as a result became classified as TDR Loans	$ 1	$ 1	$ 3	$ 3