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, 2019 USD ($)
Line of Credit Facility
Commitments	$ 2,137
Less Than One Year From The Balance Sheet Date
Line of Credit Facility
Commitments	1,022
Less Than One Year From The Balance Sheet Date | Commercial
Line of Credit Facility
Commitments	2
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	1,110
More than One and within Five Years from Balance Sheet Date | Commercial
Line of Credit Facility
Commitments	$ 2