Loans - Trouble Debt Restructuring Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	$ 1,275	$ 1,274
Trouble debt restructuring interest income recognized	15	11
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	326	411
Trouble debt restructuring interest income recognized	6	3
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	264	320
Trouble debt restructuring interest income recognized	6	2
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	19	60
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	25	0
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	18	31
Trouble debt restructuring interest income recognized	0	1
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	949	863
Trouble debt restructuring interest income recognized	9	8
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	941	849
Trouble debt restructuring interest income recognized	9	8
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Modifications [Line Items]
Trouble debt restructuring average recorded investment	$ 8	$ 14