Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended	6 Months Ended	36 Months Ended
		Dec. 31, 2016	Jun. 30, 2017	Dec. 31, 2007	Sep. 30, 2017
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		$ 66,721			$ 53,675
Carrying value of swap		4,135,130			4,548,237
Carrying value		627			201
Collateral accepted under security resale agreements, fair value		30,784			18,897
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value		29,835			16,997
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales		769			1,815
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		892			2,814
Trading Securities [Member]
Guarantor Obligations [Line Items]
Securities pledged as collateral that can be sold or repledged by the secured party, fair value		2,772			3,626
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1],[2]	5,423			5,190
Carrying value	[1],[2]	0			0
Performance (non-financial) guarantees, net of participations [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1],[2]	2,969			3,257
Carrying value	[1],[2]	0			0
Obligation to Repurchase Receivables Sold [Member]
Guarantor Obligations [Line Items]
Outstanding repurchase demands		6			2
Mortgage Securitization Activity Related Litigation [Member] | HSBC Securities [Member]
Guarantor Obligations [Line Items]
Mortgage securitization outstanding loan purchase and sold		4,600			4,300
Other liabilities [Member]
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit		39			26
Other liabilities [Member] | Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Deferred fees on standby letters of credit		$ 49			50
Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Shares sold (shares)		638,219	2,391,936
Other Income (Loss) [Member] | Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Gain on sale of shares sold		$ 71	$ 312
Swap [Member]
Guarantor Obligations [Line Items]
Carrying value of swap		$ 14			52
Carrying value of swap related to sale during the first half of 2017					$ 36

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

[2] Includes $1,270 million and $1,315 million of both financial and performance standby letters of credit issued for the benefit of HSBC affiliates at September 30, 2017 and December 31, 2016, respectively.