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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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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Derivative
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	$ 261.0		$ 269.7
Derivative, Notional Amount	3,769.4		3,818.2
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	1.8
Component of Derivative Gain (Loss) Excluded from the Assessment of Hedge Effectiveness	4.7	$ 27.2
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as Fair Value Hedge	$ 0.0	$ 0.0
Cash Flow Hedge, Hedging Exposure, Maximum Period	27 years
Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	$ 3,468.6		3,498.9
Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	300.8		319.3
Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,646.0		2,730.3
Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	102.3		115.6
Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	120.0		127.3
Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	822.6		768.6
Total Return Swap \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	151.4		154.8
Total Return Swap \| Not Designated as Hedging Instrument \| Fair Value Volatility
Derivative
Derivative, Notional Amount	151.4		154.8
Total Return Swap \| Not Designated as Hedging Instrument \| Credit Spreads and Interest Rate Volatility
Derivative
Derivative, Notional Amount	0.0		700.0
Forward Benchmark Interest Rate Lock \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,526.0		2,603.0
Foreign Exchange Forward \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	47.1		48.9
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	102.3		115.6
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	120.0		127.3
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	822.6		768.6
Credit Exposure
Derivative
Credit Exposure on Derivatives	$ 0.1		$ 0.0