Financial Instruments - Schedule of Notional Amounts and Fair Values of Derivatives Outstanding (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Assets	$ 341,000,000.0	$ 103,000,000.0
Liabilities	96,200,000	139,000,000.0
Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	23,300,000	9,500,000
Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	33,600,000	13,600,000
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Assets	341,000,000.0	103,000,000.0
Liabilities	96,200,000	139,000,000.0
Derivatives Not Designated as Hedging Instruments [Member] \| Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	23,300,000	9,500,000
Assets	500,000	100,000
Liabilities	0	0
Derivatives Not Designated as Hedging Instruments [Member] \| Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	33,600,000	13,600,000
Assets	0	0
Liabilities	500,000	100,000
Designated as Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Assets	0	0
Liabilities	0	0
Interest Rate Swaps [Member] \| Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375,000,000
Interest Rate Swaps [Member] \| Cash Flow [Member] \| Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	210,000,000
Interest Rate Swaps [Member] \| Derivatives Not Designated as Hedging Instruments [Member] \| Commercial Customers [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	8,847,700,000	7,455,900,000
Assets	320,500,000	76,300,000
Liabilities	13,900,000	102,600,000
Interest Rate Swaps [Member] \| Derivatives Not Designated as Hedging Instruments [Member] \| Institutional Counterparties [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	8,851,800,000	7,161,300,000
Assets	17,100,000	22,600,000
Liabilities	78,200,000	32,400,000
Interest Rate Swaps [Member] \| Designated as Hedging Instrument [Member] \| Cash Flow [Member] \| Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	210,000,000.0	210,000,000.0
Assets	0	0
Liabilities	0	0
Interest Rate Swaps [Member] \| Designated as Hedging Instrument [Member] \| Subordinated Notes [Member] \| Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375,000,000.0	375,000,000.0
Assets	0	0
Liabilities	0	0
Interest Rate Caps [Member] \| Derivatives Not Designated as Hedging Instruments [Member] \| Commercial Customers [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	246,000,000.0	329,100,000
Assets	1,600,000	600,000
Liabilities	100,000	2,500,000
Interest Rate Caps [Member] \| Derivatives Not Designated as Hedging Instruments [Member] \| Institutional Counterparties [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	246,000,000.0	329,100,000
Assets	100,000	2,500,000
Liabilities	1,600,000	600,000
Risk Participation Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	882,800,000	576,500,000
Risk Participation Agreements [Member] \| Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	882,800,000	576,500,000
Assets	0	0
Liabilities	100,000	0
Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	180,400,000	145,200,000
Foreign Exchange Contracts [Member] \| Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	180,400,000	145,200,000
Assets	1,200,000	900,000
Liabilities	$ 1,800,000	$ 800,000

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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