Loans and Leases - Summary of Outstanding Principal Balance and Carrying Amount of Acquired Loans (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	$ 23,289	$ 22,153
Accounted for under ASC 310-30:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	2,684	3,768
Carrying amount	2,461	3,570
Accounted for under ASC 310-20:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	436	602
Carrying amount	425	513
Total loans acquired in a business combination:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	3,120	4,370
Carrying amount	$ 2,886	$ 4,083