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, 2014
Line of Credit Facility [Line Items]
Commitments	$ 3,931
Less Than One Year From The Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	2,097	[1]
Less Than One Year From The Balance Sheet Date | Commercial
Line of Credit Facility [Line Items]
Commitments	29
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,748	[1]
More than One and within Five Years from Balance Sheet Date | Commercial
Line of Credit Facility [Line Items]
Commitments	18
More than five years from balance sheet date
Line of Credit Facility [Line Items]
Commitments	$ 86

[1] Includes $29 and $18 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.