Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Line of Credit Facility [Line Items]
Commitments	$ 4,281
Financial Standby Letter of Credit
Line of Credit Facility [Line Items]
Commitments	1,831	[1]
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	2,407	[1]
More than One and within Five Years from Balance Sheet Date | Commercial [Member]
Line of Credit Facility [Line Items]
Commitments	4
One YearFrom Balance Sheet Date1 [Member] | Commercial [Member]
Line of Credit Facility [Line Items]
Commitments	$ 60

[1] Includes $60 and $4 issued on behalf of commercial customers to facilitate trade payments in U.S. dollars and foreign currencies which expire less than one year and between one and five years, respectively.