Business Segments - Summary on Reconciliation of Results Under Ifrs to Us Gaap (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017		Dec. 31, 2017
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	$ 613		$ 606
Group Reporting Basis Other operating income	[2]	448		457
Group Reporting Basis Total operating income		1,061		1,063
Group Reporting Basis Expected credit losses		(21)		(61)
Group Reporting Basis Revenues		1,082		1,124
Group Reporting Basis Operating expenses	[2]	1,285		820	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		(203)		304
Group Reporting Basis Total assets		212,865		239,793
Group Reporting Basis Total loans, net		66,090	[4]	70,572
Group Reporting Basis Goodwill		1,260		1,264
Group Reporting Basis Total deposits		103,778	[4]	95,678
Net interest income	[1]	552		597
Other operating income	[2],[5]	513		593
Total operating income		1,065		1,190
Provision for credit losses		(71)		(77)
Total income		1,136		1,267
Operating expenses	[2]	1,282		819	[3]
Income (loss) before income tax		(146)		448
Total assets		182,035	[6]	201,583		$ 187,235	[6]
Total loans, net		66,739	[4]	68,667		71,882
Goodwill		1,607		1,612		1,607
Total deposits		117,953	[4]	129,258		$ 118,702
Group Reporting Basis Adjustments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1],[7]	8		(13)
Group Reporting Basis Other operating income	[2],[7]	(11)		140
Group Reporting Basis Total operating income	[7]	(3)		127
Group Reporting Basis Expected credit losses	[7]	(51)		(27)
Group Reporting Basis Revenues	[7]	48		154
Group Reporting Basis Operating expenses	[2],[7]	(9)		10	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense	[7]	57		144
Group Reporting Basis Total assets	[7]	(30,830)		(38,255)
Group Reporting Basis Total loans, net	[7]	(683)	[4]	(323)
Group Reporting Basis Goodwill	[7]	347		348
Group Reporting Basis Total deposits	[7]	(2,803)	[4]	(4,430)
Group Reporting Basis Reclassifications [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	(69)		4
Group Reporting Basis Other operating income	[2]	76		(4)
Group Reporting Basis Total operating income		7		0
Group Reporting Basis Expected credit losses		1		11
Group Reporting Basis Revenues		6		(11)
Group Reporting Basis Operating expenses	[2]	6		(11)	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		0		0
Group Reporting Basis Total assets		0		45
Group Reporting Basis Total loans, net		1,332	[4]	(1,582)
Group Reporting Basis Goodwill		0		0
Group Reporting Basis Total deposits		16,978	[4]	38,010
Reclassification [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	0		0
Group Reporting Basis Other operating income	[2]	0		0
Group Reporting Basis Total operating income		0		0
Group Reporting Basis Expected credit losses		0		0
Group Reporting Basis Revenues		0		0
Group Reporting Basis Operating expenses	[2]	0		0	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		0		0
Group Reporting Basis Total assets		0		0
Group Reporting Basis Total loans, net		0	[4]	0
Group Reporting Basis Goodwill		0		0
Group Reporting Basis Total deposits		0	[4]	0
RBWM [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	216		213
Group Reporting Basis Other operating income	[2]	93		148
Group Reporting Basis Total operating income		309		361
Group Reporting Basis Expected credit losses		3		9
Group Reporting Basis Revenues		306		352
Group Reporting Basis Operating expenses	[2]	325		286	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		(19)		66
Group Reporting Basis Total assets		18,533		19,057
Group Reporting Basis Total loans, net		16,665	[4]	16,802
Group Reporting Basis Goodwill		581		581
Group Reporting Basis Total deposits		34,822	[4]	34,811
RBWM [Member] | Operating Segments [Member] | Restatement Adjustment [Member]
Operating Statistics [Line Items]
Group Reporting Basis Other operating income				11
Group Reporting Basis Operating expenses				11
CMB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	186		180
Group Reporting Basis Other operating income	[2]	55		52
Group Reporting Basis Total operating income		241		232
Group Reporting Basis Expected credit losses		(10)		(36)
Group Reporting Basis Revenues		251		268
Group Reporting Basis Operating expenses	[2]	151		139	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		100		129	[7]
Group Reporting Basis Total assets		24,421		24,175
Group Reporting Basis Total loans, net		23,402	[4]	23,170
Group Reporting Basis Goodwill		358		358
Group Reporting Basis Total deposits		23,573	[4]	19,914
GBM [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	149		152
Group Reporting Basis Other operating income	[2]	197		142
Group Reporting Basis Total operating income		346		294
Group Reporting Basis Expected credit losses		(14)		(35)
Group Reporting Basis Revenues		360		329
Group Reporting Basis Operating expenses	[2]	216		224	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		144		105	[7]
Group Reporting Basis Total assets		85,481		84,949
Group Reporting Basis Total loans, net		18,100	[4]	21,108
Group Reporting Basis Goodwill		0		0
Group Reporting Basis Total deposits		33,778	[4]	22,960
GBM [Member] | Operating Segments [Member] | Restatement Adjustment [Member]
Operating Statistics [Line Items]
Group Reporting Basis Other operating income				21
Group Reporting Basis Operating expenses				21
Group Reporting Basis Total loans, net		200
Group Reporting Basis Total deposits		10,800
PB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	47		53
Group Reporting Basis Other operating income	[2]	20		21
Group Reporting Basis Total operating income		67		74
Group Reporting Basis Expected credit losses		(3)		2
Group Reporting Basis Revenues		70		72
Group Reporting Basis Operating expenses	[2]	61		61	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		9		11
Group Reporting Basis Total assets		7,356		7,808
Group Reporting Basis Total loans, net		6,132	[4]	5,928
Group Reporting Basis Goodwill		321		325
Group Reporting Basis Total deposits		7,970	[4]	11,355
CC [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	15		8
Group Reporting Basis Other operating income	[2]	83		94
Group Reporting Basis Total operating income		98		102
Group Reporting Basis Expected credit losses		3		(1)
Group Reporting Basis Revenues		95		103
Group Reporting Basis Operating expenses	[2]	532		110	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		(437)		(7)
Group Reporting Basis Total assets		77,074		103,804
Group Reporting Basis Total loans, net		1,791	[4]	3,564
Group Reporting Basis Goodwill		0		0
Group Reporting Basis Total deposits		3,635	[4]	$ 6,638
CC [Member] | Operating Segments [Member] | Restatement Adjustment [Member]
Operating Statistics [Line Items]
Group Reporting Basis Total loans, net		(3,000)
Group Reporting Basis Total deposits		$ (900)

[1] Net interest income of each segment represents the difference between actual interest earned on assets and interest paid on liabilities of the segment adjusted for a funding charge or credit. Segments are charged a cost to fund assets (e.g. customer loans) and receive a funding credit for funds provided (e.g. customer deposits) based on equivalent market rates. The objective of these charges/credits is to transfer interest rate risk from the segments to one centralized unit in Balance Sheet Management and more appropriately reflect the profitability of the segments.

[2] Expenses for the segments include fully apportioned corporate overhead expenses.

[3] During the fourth quarter of 2017, we changed our presentation for certain cost reimbursements that were previously netted as an offset to affiliate expense and began presenting these reimbursements gross in affiliate income. As a result, we have reclassified prior period amounts in order to conform to the current year presentation, which increased both RBWM other operating income and RBWM operating expenses $11 million and also increased both GB&M other operating income and GB&M operating expenses $21 million during the three months ended March 31, 2017. See Note 14, "Related Party Transactions," for additional information.

[4] In addition to the changes discussed above, in conjunction with HSBC's adoption of the requirements of IFRS 9 we also adopted changes in presentation under the Group Reporting Basis related to affiliate loans and deposits as well as cash collateral posted and received. Beginning January 1, 2018, affiliate loans have been reclassified from other assets to loans, affiliate deposits have been reclassified from other liabilities to deposits, cash collateral posted has been reclassified from loans to other assets and cash collateral received has been reclassified from deposits to other liabilities. As a result of these changes, total loans, net and total deposits in the GB&M segment increased $0.2 billion and $10.8 billion, respectively, and total loans, net and total deposits in the CC segment decreased $3.0 billion and $0.9 billion, respectively, at March 31, 2018.

[5] See Note 15, "Business Segments," for a reconciliation of total other revenues on a U.S. GAAP basis to other operating income for each business segment under the Group Reporting Basis.

[6] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at March 31, 2018 and December 31, 2017 which are consolidated on our balance sheet. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 17, "Variable Interest Entities," for additional information. Assets: Other assets $146 million and $154 million. Total assets $146 million and $154 million respectively. Liabilities: Long-term debt $73 million and $73 million, Interest, taxes and other liabilities $59 million and $59 million. Total liabilities $132 million and $132 million, respectively.

[7] Represents adjustments associated with differences between U.S. GAAP and the Group Reporting Basis.