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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, 2025	Mar. 31, 2024	Dec. 31, 2024
Derivative
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	$ 220.4		$ 255.7
Derivative, Notional Amount	4,474.3		3,751.4
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	6.6
Component of Derivative Gain (Loss) Excluded from the Assessment of Hedge Effectiveness	27.2	$ (9.9)
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	28 years
Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	$ 3,474.9		3,445.5
Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	999.4		305.9
Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,728.1		2,709.1
Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	125.9		125.9
Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	139.1		139.1
Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	746.8		736.4
Forwards \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	47.3		51.1
Forwards \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,589.0		2,570.0
Total Return Swap \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	826.2		128.9
Total Return Swap \| Not Designated as Hedging Instrument \| Fair Value Volatility
Derivative
Derivative, Notional Amount	126.2		128.9
Total Return Swap \| Not Designated as Hedging Instrument \| Credit Spreads and Interest Rate Volatility
Derivative
Derivative, Notional Amount	700.0		0.0
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	125.9		125.9
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	139.1		139.1
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	746.8		736.4
Credit Exposure
Derivative
Credit Exposure on Derivatives	$ 1.3		$ 0.5