Intangible Assets (Details 3) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Residential mortgage loans serviced for others
Outstanding principal balances at period end	$ 35,095	$ 37,839
Custodial balances maintained and included in noninterest bearing deposits at period end	$ 827	$ 838

Custodial balances maintained and included in noninterest bearing deposits at period end.

No definition available.

Name:	hsbcusa_CustodialBalancesMaintainedAndIncludedInNoninterestBearingDepositsAtPeriodEnd
Namespace Prefix:	hsbcusa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant