Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party (Parenthetical) (Detail) - Letters of Credit $ in Millions	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Commitments	$ 3,055
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	28
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility [Line Items]
Commitments	1,301	[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	$ 15

[1] Includes $28 and $15 issued on behalf of commercial customers to facilitate trade payments in U.S. dollars and foreign currencies which expire less than 1 year and between 1 and 5 years, respectively.