Derivative Financial Instruments (Narrative) (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) derivative_instrument	Nov. 08, 2021 USD ($) derivative_instrument	Dec. 31, 2020 derivative_instrument	Sep. 30, 2020 derivative_instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount to be reclassified from accumulated other comprehensive income to interest expense in the next twelve months	$ 14.9
Net derivative liability position, aggregate fair value	115.7
Interest rate contract | Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	1,000.0
Interest rate contract, qualified borrowers | Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	9,200.0
Forward commitments to sell mortgage loans | Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	1,300.0
Interest rate lock commitments | Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	624.8
Foreign exchange contracts | Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	$ 19.3
Covered call options | Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of derivative instruments held | derivative_instrument	0		0	0
Mortgage banking derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Number of derivative instruments held | derivative_instrument	0
Interest rate derivatives designated as Cash Flow Hedges | Interest Rate Swap | Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instrument	27
Interest rate derivatives designated as Cash Flow Hedges | Interest Rate Collar | Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instrument	1
Interest rate derivatives designated as Fair Value Hedges | Interest Rate Swap | Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instrument	15
Notional amount	$ 229.6
Interest rate derivatives designated as Fair Value Hedges | Interest Rate Swap | Designated as hedging instrument | Subsequent Event
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instrument		1
Notional amount		$ 73.9