Derivatives and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Derivative [Line Items]
Gross gains	$ 57.6	$ 2.1
Notional Amount	66,479.0	53,183.0	$ 64,692.0
Collateral posted by this counterparty	285.0	194.0	382.0
Interest rate contracts \| U.S. Treasury securities
Derivative [Line Items]
Gross gains	18.7
Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	5,708.0	4,335.0	7,216.0
Cumulative basis adjustment	(17.0)		8.0
Interest income related to amortization of cumulative basis adjustment (less than for current period)	0.4	0.1
Designated as Hedging Instrument \| Interest rate swap, terminated
Derivative [Line Items]
Notional amount terminated during period	1,300.0
Cumulative basis adjustment during period	(18.6)
Designated as Hedging Instrument \| Interest rate contracts
Derivative [Line Items]
Notional Amount	5,708.0	$ 4,335.0	7,216.0
Designated as Hedging Instrument \| Portfolio layer method swaps
Derivative [Line Items]
Notional Amount	2,000.0
Cumulative basis adjustment	19.0
Carrying value of hedged assets	$ 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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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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