Commitments (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, 2016 USD ($)
Line of Credit Facility
Commitments	$ 2,583
One Year From Balance Sheet Date | Commercial | Commercial customers to facilitate trade payments in U.S. dollars and foreign currencies
Line of Credit Facility
Commitments	18
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	1,164	[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
Commitments	3
More than Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	$ 32

[1] (a) Includes $ 18 and $ 3 issue d 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 - 5 years, respectively.