Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party (Parenthetical) (Detail) (Financial Standby Letter of Credit, USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Line of Credit Facility [Line Items]
Commitments	$ 4,558
One Year from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	2,130	[1]
One Year from Balance Sheet Date | Commercial [Member]
Line of Credit Facility [Line Items]
Commitments	77
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	2,361	[1]
More than One and within Five Years from Balance Sheet Date | Commercial [Member]
Line of Credit Facility [Line Items]
Commitments	$ 1

[1] Includes $77 and $1 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.