Loans - Schedule of Additional Information on Nonaccrual Loans (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Receivables [Abstract]
Interest income that would have been recorded if the nonaccrual receivable had been current in accordance with contractual terms during the period	$ 18	$ 8
Interest income that was recorded on nonaccrual loans and included in interest income during the period	$ 15	$ 7

Loans and Leases Receivable, Impaired, Interest Recorded and Interest Lost on Nonaccrual Loans

No definition available.

Name:	hsbcusa_LoansandLeasesReceivableImpairedInterestRecordedandInterestLostonNonaccrualLoans
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration