Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Total	$ 197	$ 346	$ 555
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	31	114	99
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	5	59	78
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	16	4	21
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	0	51	0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total	10	0	0
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	166	232	456
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	157	225	451
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Impaired [Line Items]
Total	4	5	1
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 5	$ 2	$ 4