Derivative Financial Instruments - Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding (Detail)	Sep. 30, 2020
Weighted Average Interest Rate Paid [Member]
Short-duration insurance contracts, discounted liabilities [Line Items]
Fair value hedge loan/lease interest rate swaps	3.39%
Weighted-Average Interest Rate Received [Member]
Short-duration insurance contracts, discounted liabilities [Line Items]
Fair value hedge loan/lease interest rate swaps	0.15%
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Short-duration insurance contracts, discounted liabilities [Line Items]
Non-hedging interest rate swaps – financial institution counterparties	4.00%
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Short-duration insurance contracts, discounted liabilities [Line Items]
Non-hedging interest rate swaps – financial institution counterparties	1.93%
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Short-duration insurance contracts, discounted liabilities [Line Items]
Non-hedging interest rate swaps – customer counterparties	1.93%
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Short-duration insurance contracts, discounted liabilities [Line Items]
Non-hedging interest rate swaps – customer counterparties	4.00%