Loans and Leases - Summary of Outstanding Principal Balance and Carrying Amount of Acquired Loans (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	$ 22,153	$ 20,999
Accounted for under ASC 310-30:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	3,768	5,176
Carrying amount	3,570	4,834
Accounted for under ASC 310-20:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	602	835
Carrying amount	513	813
Total loans acquired in a business combination:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	4,370	6,011
Carrying amount	$ 4,083	$ 5,647