Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Line of Credit Facility
Commitments	$ 4,191
Less Than One Year From The Balance Sheet Date | Financial Standby Letter of Credit
Line of Credit Facility
Commitments	1,798	[1]
More than One and within Five Years from Balance Sheet Date | Financial Standby Letter of Credit
Line of Credit Facility
Commitments	2,336	[1]
More than five years from balance sheet date | Financial Standby Letter of Credit
Line of Credit Facility
Commitments	$ 57

[1] Includes $91 and $5 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.