Loans - Delinquency Ratio for Consumer Loan (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Receivables [Abstract]
Residential Mortgage Loan Delinquency Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell	$ 967	$ 1,074

Residential mortgage loan delinquency carried at lower of amortized cost or fair value less cost to sell.

No definition available.

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