Loans and Leases - Summary of Payment Status of Originated TDRs (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	$ 48	$ 53
Performing
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	18	20
Non-Performing
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	21	23
Non-accrual
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	9	10
Originated Loans and Leases
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	44	50
Originated Loans and Leases | Performing
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	18	20
Originated Loans and Leases | Non-Performing
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	17	20
Originated Loans and Leases | Non-accrual
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	9	10
Loans Acquired in a Business Combination
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	4	3
Loans Acquired in a Business Combination | Performing
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	0	0
Loans Acquired in a Business Combination | Non-Performing
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	4	3
Loans Acquired in a Business Combination | Non-accrual
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings ("TDRs")	$ 0	$ 0