Intangible Assets - Residential Mortgage Loans Serviced for Others (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Outstanding principal balances at period end	$ 28,211	$ 32,041
Custodial balances maintained and included in noninterest bearing deposits at period end	$ 0	$ 810

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

No definition available.

Name:	husi_CustodialBalancesMaintainedAndIncludedInNoninterestBearingDepositsAtPeriodEnd
Namespace Prefix:	husi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant