Derivative Financial Instruments - Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding (Detail)	Sep. 30, 2013
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair value hedge loan/lease interest rate swaps	2.73%
Cash flow hedge interest rate swaps on junior subordinated deferrable interest debentures	5.47%
Weighted Average Interest Rate Paid [Member] | Financial Institution Counterparties [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps	4.36%
Weighted Average Interest Rate Paid [Member] | Customer Counterparties [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps	1.81%
Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Fair value hedge loan/lease interest rate swaps	0.18%
Cash flow hedge interest rate swaps on junior subordinated deferrable interest debentures	1.81%
Weighted-Average Interest Rate Received [Member] | Financial Institution Counterparties [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps	1.81%
Weighted-Average Interest Rate Received [Member] | Customer Counterparties [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps	4.36%