Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Impaired [Line Items]
Total	$ 45	$ 144	$ 150	$ 256
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	5	80	26	100
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	0	15
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	5	29	16	34
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Total	0	51	0	51
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Total	0	0	10	0
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Total	40	64	124	156
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Total	38	63	117	152
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Impaired [Line Items]
Total	1	1	3	3
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Total	$ 1	$ 0	$ 4	$ 1