Organization and Presentation Organization and Presentation (Details) $ in Millions	6 Months Ended
Jun. 30, 2017 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Income tax expense out of period adjustment	$ (9)

Income Tax Expense (Benefit), Out of Period Adjustment

No definition available.

Name:	hsbcusa_IncomeTaxExpenseBenefitOutofPeriodAdjustment
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration