Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party (Detail) (Financial Standby Letter of Credit, USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Line of Credit Facility [Line Items]
Commitments	$ 3,781
Less Than One Year From The Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	2,245	[1]
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,484	[1]
More than five years from balance sheet date
Line of Credit Facility [Line Items]
Commitments	$ 52

[1] Includes $84 and $22 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.