Fair Value Option - Components of Gain (Loss) on Instruments at Fair Value and Related Derivatives (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Gain (loss) on related derivatives	$ 568	$ 449	$ 348	$ 268
Gain (loss) on instruments designated at fair value and related derivatives	(12)	(1)	(17)	(4)
Income Statement Location [Axis]: hsbcusa:GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(587)	(457)	(381)	(285)
Credit risk component, total	(18)	(1)	(20)	(8)
Total mark-to-market on financial instruments designated at fair value	(605)	(458)	(401)	(293)
Gain (loss) on related derivatives	593	457	384	289
Gain (loss) on instruments designated at fair value and related derivatives	(12)	(1)	(17)	(4)
Loans \| Income Statement Location [Axis]: hsbcusa:GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	0	0	0	0
Credit risk component, assets	(18)	(1)	(20)	(8)
Total mark-to-market on financial instruments designated at fair value	(18)	(1)	(20)	(8)
Gain (loss) on related derivatives	0	0	0	0
Gain (loss) on instruments designated at fair value and related derivatives	(18)	(1)	(20)	(8)
Long-term debt \| Income Statement Location [Axis]: hsbcusa:GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	8	(5)	13	(21)
Credit risk component, liabilities	0	0	0	0
Total mark-to-market on financial instruments designated at fair value	8	(5)	13	(21)
Gain (loss) on related derivatives	(8)	7	(12)	25
Gain (loss) on instruments designated at fair value and related derivatives	0	2	1	4
Hybrid Instruments \| Income Statement Location [Axis]: hsbcusa:GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative
Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]
Interest rate and other components	(595)	(452)	(394)	(264)
Credit risk component, liabilities	0	0	0	0
Total mark-to-market on financial instruments designated at fair value	(595)	(452)	(394)	(264)
Gain (loss) on related derivatives	601	450	396	264
Gain (loss) on instruments designated at fair value and related derivatives	$ 6	$ (2)	$ 2	$ 0

Components Of Gain On Instruments At Fair Value And Related Derivatives [Line Items]

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Fair Value, Option, Credit Risk, Gains (Losses), Net

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Fair Value, Option, Interest Rate And Other Components, Gains (Losses)

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Fair value changes on fixed rate debt, loans and certain other financial instruments accounted for under fair value option as well as the fair value changes on the related derivatives and realized gains (losses) on the debt related derivatives.

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

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This item represents the estimated amount of gains or losses included in earnings during the period attributable to changes in instrument-specific credit risk arising from loans and other receivables held as assets.

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Amount, before tax, after reclassification adjustment, of gain (loss) from increase (decrease) in instrument-specific credit risk of financial liability measured under fair value option.

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