Loans - Status of Commercial Loan Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Nonaccrual Loans	$ 1,466	$ 1,629
Accruing Loans Contractually Past Due 90 days or More	40	80
Total loans	62,932	63,258	53,869
Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	43,307	43,650
Nonaccrual Loans	327	463
Accruing Loans Contractually Past Due 90 days or More	5	37
Total loans	43,639	44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	8,052	8,064
Nonaccrual Loans	265	385
Accruing Loans Contractually Past Due 90 days or More	2	8
Total loans	8,319	8,457	7,777
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	12,693	12,533
Nonaccrual Loans	30	47
Accruing Loans Contractually Past Due 90 days or More	2	28
Total loans	12,725	12,608	10,889
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	19,700	19,991
Nonaccrual Loans	18	18
Accruing Loans Contractually Past Due 90 days or More	0	0
Total loans	19,718	20,009	13,852
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	2,862	3,062
Nonaccrual Loans	14	13
Accruing Loans Contractually Past Due 90 days or More	1	1
Total loans	$ 2,877	$ 3,076	$ 3,051