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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Impaired [Line Items]
Total	$ 136	$ 45	$ 276	$ 150
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	87	5	154	26
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	4	0
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	87	5	137	16
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	13	0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	0	10
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	49	40	122	124
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	47	38	117	117
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Total	1	1	2	3
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 1	$ 1	$ 3	$ 4