Loans - Status of Commercial Loan Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Nonaccrual Loans	$ 1,403	$ 1,629
Accruing Loans Contractually Past Due 90 days or More	40	80
Total loans	66,705	63,258	56,064
Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	47,010	43,650
Nonaccrual Loans	246	463
Accruing Loans Contractually Past Due 90 days or More	8	37
Total loans	47,264	44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	8,349	8,064
Nonaccrual Loans	179	385
Accruing Loans Contractually Past Due 90 days or More	1	8
Total loans	8,529	8,457	7,977
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	12,341	12,533
Nonaccrual Loans	44	47
Accruing Loans Contractually Past Due 90 days or More	6	28
Total loans	12,391	12,608	11,256
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	23,321	19,991
Nonaccrual Loans	18	18
Accruing Loans Contractually Past Due 90 days or More	0	0
Total loans	23,339	20,009	15,042
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	2,999	3,062
Nonaccrual Loans	5	13
Accruing Loans Contractually Past Due 90 days or More	1	1
Total loans	$ 3,005	$ 3,076	$ 3,142