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	Dec. 31, 2011
Line of Credit Facility [Line Items]
Commitments	$ 4,744
One Year from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,940	[1]
One Year from Balance Sheet Date | Commercial [Member]
Line of Credit Facility [Line Items]
Commitments	75
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	2,665	[1]
More than One and within Five Years from Balance Sheet Date | Commercial [Member]
Line of Credit Facility [Line Items]
Commitments	$ 3

[1] Includes $75 and $3 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.