Business Segments - Summary on Reconciliation of Results Under Ifrs to Us Gaap (Detail) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017		Dec. 31, 2017
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	$ 632		$ 607		$ 1,245		$ 1,213
Group Reporting Basis Other operating income		469		558		917	[2]	1,015	[2]
Group Reporting Basis Total operating income		1,101		1,165		2,162		2,228
Group Reporting Basis Expected credit losses		(175)		(9)		(196)		(70)
Group Reporting Basis Revenues		1,276		1,174		2,358		2,298
Group Reporting Basis Operating expenses	[2]	804		864		2,089		1,684	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		472		310		269		614
Group Reporting Basis Total assets		214,855		228,982		214,855		228,982
Group Reporting Basis Total loans, net		65,261	[4]	68,495		65,261	[4]	68,495
Group Reporting Basis Goodwill		1,260		1,264		1,260		1,264
Group Reporting Basis Total deposits		101,729	[4]	94,421		101,729	[4]	94,421
Net interest income	[1]	555		582		1,107		1,179
Other operating income	[5]	537		558		1,050	[2]	1,151	[2]
Total operating income		1,092		1,140		2,157		2,330
Provision for credit losses		(45)		(21)		(116)		(98)
Total income		1,137		1,161		2,273		2,428
Operating expenses	[2]	786		849		2,068		1,668	[3]
Income before income tax		351		312		205		760
Total assets		180,687	[6]	193,350		180,687	[6]	193,350		$ 187,235	[6]
Total loans, net		65,868	[4]	67,215		65,868	[4]	67,215		71,882
Goodwill		1,607		1,612		1,607		1,612		1,607
Total deposits		114,355	[4]	117,143		114,355	[4]	117,143		$ 118,702
Group Reporting Basis Adjustments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	6	[7]	(16)	[7]	14	[8]	(29)	[8]
Group Reporting Basis Other operating income		(9)	[7]	(11)	[7]	(20)	[2],[8]	129	[2],[8]
Group Reporting Basis Total operating income		(3)	[7]	(27)	[7]	(6)	[8]	100	[8]
Group Reporting Basis Expected credit losses		118	[7]	(21)	[7]	67	[8]	(48)	[8]
Group Reporting Basis Revenues		(121)	[7]	(6)	[7]	(73)	[8]	148	[8]
Group Reporting Basis Operating expenses	[2]	0	[7]	(8)	[7]	(9)	[8]	2	[3],[8]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		(121)	[7]	2	[7]	(64)	[8]	146	[8]
Group Reporting Basis Total assets	[8]	(34,168)		(35,632)		(34,168)		(35,632)
Group Reporting Basis Total loans, net	[8]	(1,341)	[4]	(1,035)		(1,341)	[4]	(1,035)
Group Reporting Basis Goodwill	[8]	347		348		347		348
Group Reporting Basis Total deposits	[8]	(3,168)	[4]	(3,849)		(3,168)	[4]	(3,849)
Group Reporting Basis Reclassifications [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	(83)		(9)		(152)		(5)
Group Reporting Basis Other operating income		77		11		153	[2]	7	[2]
Group Reporting Basis Total operating income		(6)		2		1		2
Group Reporting Basis Expected credit losses		12		9		13		20
Group Reporting Basis Revenues		(18)		(7)		(12)		(18)
Group Reporting Basis Operating expenses	[2]	(18)		(7)		(12)		(18)	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		0		0		0		0
Group Reporting Basis Total assets		0		0		0		0
Group Reporting Basis Total loans, net		1,948	[4]	(245)		1,948	[4]	(245)
Group Reporting Basis Goodwill		0		0		0		0
Group Reporting Basis Total deposits		15,794	[4]	26,571		15,794	[4]	26,571
Reclassification [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	0		0		0		0
Group Reporting Basis Other operating income		0		0		0	[2]	0	[2]
Group Reporting Basis Total operating income		0		0		0		0
Group Reporting Basis Expected credit losses		0		0		0		0
Group Reporting Basis Revenues		0		0		0		0
Group Reporting Basis Operating expenses	[2]	0		0		0		0	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		0		0		0		0
Group Reporting Basis Total assets		0		0		0		0
Group Reporting Basis Total loans, net		0	[4]	0		0	[4]	0
Group Reporting Basis Goodwill		0		0		0		0
Group Reporting Basis Total deposits		0	[4]	0		0	[4]	0
RBWM [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	225		221		441		434
Group Reporting Basis Other operating income		71		238		164	[2]	386	[2]
Group Reporting Basis Total operating income		296		459		605		820
Group Reporting Basis Expected credit losses		3		(3)		6		6
Group Reporting Basis Revenues		293		462		599		814
Group Reporting Basis Operating expenses	[2]	341		287		666		573	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		(48)		175		(67)		241
Group Reporting Basis Total assets		18,691		18,960		18,691		18,960
Group Reporting Basis Total loans, net		16,695	[4]	16,709		16,695	[4]	16,709
Group Reporting Basis Goodwill		581		581		581		581
Group Reporting Basis Total deposits		32,672	[4]	34,868		32,672	[4]	34,868
CMB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	195		181		381		361
Group Reporting Basis Other operating income		58		52		113	[2]	104	[2]
Group Reporting Basis Total operating income		253		233		494		465
Group Reporting Basis Expected credit losses		(36)		(5)		(46)		(41)
Group Reporting Basis Revenues		289		238		540		506
Group Reporting Basis Operating expenses	[2]	139		141		290		280	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		150		97		250		226	[8]
Group Reporting Basis Total assets		23,851		23,515		23,851		23,515
Group Reporting Basis Total loans, net		22,879	[4]	22,335		22,879	[4]	22,335
Group Reporting Basis Goodwill		358		358		358		358
Group Reporting Basis Total deposits		23,643	[4]	20,799		23,643	[4]	20,799
GBM [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	151		156		300		308
Group Reporting Basis Other operating income		252		169		449	[2]	311	[2]
Group Reporting Basis Total operating income		403		325		749		619
Group Reporting Basis Expected credit losses		(143)		(2)		(157)		(37)
Group Reporting Basis Revenues		546		327		906		656
Group Reporting Basis Operating expenses	[2]	209		248		425		472	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		337		79		481		184	[8]
Group Reporting Basis Total assets		79,535		80,426		79,535		80,426
Group Reporting Basis Total loans, net		17,786	[4]	19,805		17,786	[4]	19,805
Group Reporting Basis Goodwill		0		0		0		0
Group Reporting Basis Total deposits		32,749	[4]	20,920		32,749	[4]	20,920
PB [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	43		56		90		109
Group Reporting Basis Other operating income		16		21		36	[2]	42	[2]
Group Reporting Basis Total operating income		59		77		126		151
Group Reporting Basis Expected credit losses		0		1		(3)		3
Group Reporting Basis Revenues		59		76		129		148
Group Reporting Basis Operating expenses	[2]	61		63		122		124	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		(2)		13		7		24
Group Reporting Basis Total assets		7,075		8,131		7,075		8,131
Group Reporting Basis Total loans, net		6,036	[4]	6,354		6,036	[4]	6,354
Group Reporting Basis Goodwill		321		325		321		325
Group Reporting Basis Total deposits		8,112	[4]	10,262		8,112	[4]	10,262
CC [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Net interest income	[1]	18		(7)		33		1
Group Reporting Basis Other operating income		72		78		155	[2]	172	[2]
Group Reporting Basis Total operating income		90		71		188		173
Group Reporting Basis Expected credit losses		1		0		4		(1)
Group Reporting Basis Revenues		89		71		184		174
Group Reporting Basis Operating expenses	[2]	54		125		586		235	[3]
Group Reporting Basis Profit (Loss) Before Income Tax Expense		35		(54)		(402)		(61)
Group Reporting Basis Total assets		85,703		97,950		85,703		97,950
Group Reporting Basis Total loans, net		1,865	[4]	3,292		1,865	[4]	3,292
Group Reporting Basis Goodwill		0		0		0		0
Group Reporting Basis Total deposits		4,553	[4]	7,572		4,553	[4]	7,572
Restatement Adjustment [Member] | RBWM [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Other operating income				13				24
Group Reporting Basis Operating expenses				13				24
Restatement Adjustment [Member] | GBM [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Other operating income				16				37
Group Reporting Basis Operating expenses				$ 16				$ 37
Group Reporting Basis Total loans, net		100				100
Group Reporting Basis Total deposits		8,400				8,400
Restatement Adjustment [Member] | CC [Member] | Operating Segments [Member]
Operating Statistics [Line Items]
Group Reporting Basis Total loans, net		(2,300)				(2,300)
Group Reporting Basis Total deposits		$ (1,100)				$ (1,100)

[1] Net interest income of each segment represents the difference between actual interest earned on assets and interest incurred 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 $13 million and $24 million and also increased both GB&M other operating income and GB&M operating expenses $16 million and $37 million during the three and six months ended June 30, 2017, respectively. 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 $0.1 billion and $8.4 billion, respectively, and total loans, net and total deposits in the CC segment decreased $2.3 billion and $1.1 billion, respectively, at June 30, 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 June 30, 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 $136 million and $154 million. Total assets $136 million and $154 million respectively. Liabilities: Long-term debt $73 million and $73 million, Interest, taxes and other liabilities $57 million and $59 million. Total liabilities $130 million and $132 million, respectively.

[7] Represents differences in financial statement presentation between U.S. GAAP and the Group Reporting Basis.

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