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Fair value of derivative asset subject to concentration of credit or market risk or both.

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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

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Amount of net gain (loss) recognized in earnings when a hedged firm commitment no longer qualifies as a fair value hedge.

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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Derivative
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	$ 147.0		$ 116.2
Derivative, Notional Amount	3,094.0		2,983.7
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	13.2
Component of Derivative Gain (Loss) Excluded from the Assessment of Hedge Effectiveness	(9.9)	$ 2.5
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as Fair Value Hedge	$ 0.0	$ 0.0
Maximum Length of Time Hedged in Cash Flow Hedge	39 years
Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	$ 2,796.0		2,697.0
Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	298.0		286.7
Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,153.5		2,054.5
Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	132.0		132.0
Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	149.5		149.5
Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	642.5		642.5
Forwards \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	53.5		52.5
Forwards \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,004.0		1,905.0
Total Return Swap \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	112.5		102.2
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	132.0		132.0
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	149.5		149.5
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	642.5
Credit Exposure
Derivative
Credit Exposure on Derivatives	$ 1.5		$ 1.6