Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Additional Information (Detail) - USD ($) $ in Millions		36 Months Ended
		Dec. 31, 2007	Sep. 30, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 114,532	$ 128,894
Collateral accepted under security resale agreements, fair value			21,589	7,165
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value			15,189	6,765
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales			362	2,226
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			3,547	8,348
Trading Securities [Member]
Guarantor Obligations [Line Items]
Securities pledged as collateral that can be sold or repledged by the secured party, fair value			3,126	2,886
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	[1],[2]		5,873	5,358
Performance (non-financial) guarantees, net of participations [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	[1],[2]		3,159	3,083
Liquidity asset purchase agreements [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	[1]		3,097	2,685
Mortgage Securitization Activity Related Litigation [Member] | Hsbc Securities [Member]
Guarantor Obligations [Line Items]
Mortgage Securitization Outstanding Loan Purchase And Sold			5,300	5,700
Other liabilities [Member]
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit			18	16
Other liabilities [Member] | Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Deferred fees on standby letters of credit			$ 47	$ 50

[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 $897 million and $937 million issued for the benefit of HSBC affiliates at September 30, 2015 and December 31, 2014, respectively.