Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Additional Information (Detail) - USD ($) $ in Millions		36 Months Ended
		Dec. 31, 2007	Sep. 30, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss			$ 76,674	$ 103,647
Collateral accepted under security resale agreements, fair value			32,118	25,058
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value			26,478	19,558
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales			1,409	3,400
HSBC Securities [Member]
Guarantor Obligations [Line Items]
Whole loan securitization		$ 24,000
Securities available-for-sale [Member]
Guarantor Obligations [Line Items]
Securities pledged as collateral that can be sold or repledged by the secured party, fair value			658	1,000
Trading Securities [Member]
Guarantor Obligations [Line Items]
Securities pledged as collateral that can be sold or repledged by the secured party, fair value			3,323	3,797
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1],[2]		5,539	5,842
Performance (non-financial) guarantees, net of participations [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1],[2]		2,887	3,008
Liquidity asset purchase agreements [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1]		0	3,362
Mortgage Securitization Activity Related Litigation [Member] | HSBC Securities [Member]
Guarantor Obligations [Line Items]
Mortgage securitization outstanding loan purchase and sold			4,800	5,200
Obligation to Repurchase Receivables Sold [Member]
Guarantor Obligations [Line Items]
Outstanding Repurchase Demands			9	5
Other liabilities [Member]
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit			38	19
Other liabilities [Member] | Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Deferred fees on standby letters of credit			$ 49	$ 54

[1] For standby letters of credit and liquidity asset purchase agreements, maximum loss represents losses to be recognized assuming the letter of credit and liquidity facilities have been fully drawn and the obligors have defaulted with zero recovery.

[2] Includes $1,204 million and $910 million issued for the benefit of HSBC affiliates at September 30, 2016 and December 31, 2015, respectively.