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, 2014
Line of Credit Facility [Line Items]
Commitments	$ 3,974
One Year From Balance Sheet Date | Commercial | Commercial customers to facilitate trade payments in U.S. dollars and foreign currencies
Line of Credit Facility [Line Items]
Commitments	88
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,750	[1]
More than One and within Five Years from Balance Sheet Date | Commercial | Commercial customers to facilitate trade payments in U.S. dollars and foreign currencies
Line of Credit Facility [Line Items]
Commitments	$ 17

[1] Includes $88 and $17 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.