Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended			36 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2007
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss		$ 51,036	$ 66,721
Carrying value of swap		4,793,784	4,135,130
Net rental expense		148	140	$ 143
Carrying value		(303)	627
Collateral accepted under security resale agreements, fair value		34,759	30,784
Collateral accepted under security repurchase agreements but not reported on the balance sheet that can be sold or repledged, fair value		32,459	29,835
Collateral accepted under security repurchase agreements that has been sold or repledged under repurchase agreements or to cover short sales		1,231	769
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		524	892
Trading Securities [Member]
Guarantor Obligations [Line Items]
Securities pledged as collateral that can be sold or repledged by the secured party, fair value		3,185	2,772
Financial standby letters of credit, net of participations [Member]
Guarantor Obligations [Line Items]
Notional/maximum exposure to loss	[1],[2]	5,128	5,423
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]	3,580	2,969
Carrying value	[1],[2]	0	0
Obligation to Repurchase Receivables Sold [Member]
Guarantor Obligations [Line Items]
Outstanding repurchase demands		3	6	$ 5
Other liabilities [Member]
Guarantor Obligations [Line Items]
Allowance for credit losses on unfunded standby letters of credit		26	39
Other liabilities [Member] | Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Deferred fees on standby letters of credit		$ 48	$ 49
Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Shares sold (shares)		2,391,936	638,219
Other Income (Loss) [Member] | Visa Class B Shares [Member]
Guarantor Obligations [Line Items]
Gain on sale of shares sold		$ 312	$ 71
Swap [Member]
Guarantor Obligations [Line Items]
Carrying value of swap		52	$ 14
Carrying value of swap related to sale during 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 $1,264 million and $1,315 million of both financial and performance standby letters of credit issued for the benefit of HSBC affiliates at December 31, 2017 and 2016, respectively.