Derivative Financial Instruments (Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding) (Detail)	Dec. 31, 2017
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	3.09%
Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	1.47%
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	3.93%
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	2.97%
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - customer counterparties	2.97%
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - customer counterparties	3.93%