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 $ in Millions	Sep. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Commitments	$ 3,323
Less Than One Year From The Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,914	[1]
Less Than One Year From The Balance Sheet Date | Commercial
Line of Credit Facility [Line Items]
Commitments	64
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,355	[1]
More than One and within Five Years from Balance Sheet Date | Commercial
Line of Credit Facility [Line Items]
Commitments	15
More than five years from balance sheet date
Line of Credit Facility [Line Items]
Commitments	$ 54

[1] Includes $64 and $15 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.