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, 2018 USD ($)
Line of Credit Facility
Commitments	$ 2,041
Less Than One Year From The Balance Sheet Date
Line of Credit Facility
Commitments	1,044	[1]
Less Than One Year From The Balance Sheet Date | Commercial | Commercial customers to facilitate trade payments in U.S. dollars and foreign currencies
Line of Credit Facility
Commitments	1
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	989	[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	18
More than Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	$ 8

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