Loans - Status of Commercial Loan Portfolio (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Nonaccrual Loans	$ 1,360,000,000	$ 1,629,000,000
Accruing Loans Contractually Past Due 90 days or More	46,000,000	80,000,000
Total loans	67,710,000,000	63,258,000,000	61,452,000,000
Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	48,290,000,000	43,650,000,000
Nonaccrual Loans	210,000,000	463,000,000
Accruing Loans Contractually Past Due 90 days or More	9,000,000	37,000,000
Total loans	48,509,000,000	44,150,000,000
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	8,772,000,000	8,064,000,000
Nonaccrual Loans	147,000,000	385,000,000
Accruing Loans Contractually Past Due 90 days or More	0	8,000,000
Total loans	8,919,000,000	8,457,000,000	7,920,000,000
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	13,621,000,000	12,533,000,000
Nonaccrual Loans	47,000,000	47,000,000
Accruing Loans Contractually Past Due 90 days or More	0	28,000,000
Total loans	13,668,000,000	12,608,000,000	12,497,000,000
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	23,356,000,000	19,991,000,000
Nonaccrual Loans	14,000,000	18,000,000
Accruing Loans Contractually Past Due 90 days or More	0	0
Total loans	23,370,000,000	20,009,000,000	19,011,000,000
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	2,541,000,000	3,062,000,000
Nonaccrual Loans	2,000,000	13,000,000
Accruing Loans Contractually Past Due 90 days or More	9,000,000	1,000,000
Total loans	$ 2,552,000,000	$ 3,076,000,000	$ 3,140,000,000