Derivatives and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Derivative [Line Items]
Gross gains	$ 1.4	$ 11.8	$ 59.0	$ 13.9
Notional Amount	67,895.0	51,706.0	67,895.0	51,706.0	$ 64,692.0
Collateral posted by this counterparty	261.0	399.0	261.0	399.0	382.0
Interest rate contracts \| U.S. Treasury securities
Derivative [Line Items]
Gross gains		7.7	18.7	7.7
Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	5,706.0	6,033.0	5,706.0	6,033.0	7,216.0
Cumulative basis adjustment	(30.0)		(30.0)		8.0
Interest income related to amortization of cumulative basis adjustment (less than for current period)	0.6	0.1	0.9	0.1
Designated as Hedging Instrument \| Interest rate swap, terminated
Derivative [Line Items]
Notional amount terminated during period		1,000.0	1,300.0	1,000.0
Cumulative basis adjustment during period		(11.0)	(18.6)	(11.0)
Designated as Hedging Instrument \| Interest rate contracts
Derivative [Line Items]
Notional Amount	5,706.0	6,033.0	5,706.0	6,033.0	7,216.0
Designated as Hedging Instrument \| Portfolio layer method swaps
Derivative [Line Items]
Notional amount terminated during period	0.0	500.0	2,000.0	500.0
Cumulative basis adjustment during period		$ 1.0	19.0	$ 1.0
Carrying value of hedged assets	$ 23.0		$ 23.0		$ 5.0

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Nominal or face amount used to calculate payment on derivative.

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Amount of asset hedged in fair value hedging relationship.

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Amount of increase (decrease) in interest income for hedge basis adjustment from hedged layer exceeding outstanding amount of closed portfolio of financial asset or beneficial interest secured by financial instrument.

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