Organization and Presentation Organization and Presentation (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Compensation and benefits, out of period adjustment	$ 7	$ 7
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