v3.26.1
Derivative Financial Instruments - Gains and Losses on Derivative Instruments Held For Other Purpose (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives $ 568 $ 449 $ 348 $ 268
Interest rate contracts        
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives (11) 2 (22) 34
Credit contracts        
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives (14) (6) (18) (9)
Other Contracts        
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives (11) (2) (18) (9)
Income Statement Location [Axis]: us-gaap:OtherOperatingIncomeExpenseNet | Equity contracts        
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives 0 0 0 (3)
Income Statement Location [Axis]: hsbcusa:GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative        
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives 593 457 384 289
Income Statement Location [Axis]: hsbcusa:GainLossOnInstrumentsDesignatedAtFairValueAndRelatedDerivative | Equity contracts        
Derivatives, Fair Value [Line Items]        
Gain (Loss) Recognized in Income on Derivatives $ 604 $ 455 $ 406 $ 255