Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017		Dec. 31, 2016		Mar. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 1,017	$ 912
Provision charged (credited) to income		(77)	157
Charge offs		(36)	(56)
Recoveries		17	10
Net (charge offs) recoveries		(19)	(46)
Balance at end of period		921	1,023
Ending balance: collectively evaluated for impairment				$ 645				$ 734
Ending balance: individually evaluated for impairment				276				289
Total allowances for credit losses		1,017	912	921		$ 1,017		1,023
Collectively evaluated for impairment	[1]			67,545				79,660
Individually evaluated for impairment	[2]			993				914
Loans carried at the lower of amortized cost or fair value less cost to sell				1,050				1,158
Total loans				69,588		73,875		81,732
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans				49,996		54,216
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		92	86
Provision charged (credited) to income		1	9
Charge offs		(1)	0
Recoveries		0	0
Net (charge offs) recoveries		(1)	0
Balance at end of period		92	95
Ending balance: collectively evaluated for impairment				86				94
Ending balance: individually evaluated for impairment				6				1
Total allowances for credit losses		92	86	92		92		95
Collectively evaluated for impairment	[1]			10,758				10,067
Individually evaluated for impairment	[2]			44				103
Loans carried at the lower of amortized cost or fair value less cost to sell				0				0
Total loans				10,802		10,890		10,170
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[3]	317	407
Provision charged (credited) to income	[3]	(42)	(47)
Charge offs	[3]	(21)	(28)
Recoveries	[3]	12	2
Net (charge offs) recoveries	[3]	(9)	(26)
Balance at end of period	[3]	266	334
Ending balance: collectively evaluated for impairment	[3]			230				251
Ending balance: individually evaluated for impairment	[3]			36				83
Total allowances for credit losses	[3]	317	407	266		317		334
Collectively evaluated for impairment	[1],[3]			12,828				14,364
Individually evaluated for impairment	[2],[3]			324				306
Loans carried at the lower of amortized cost or fair value less cost to sell	[3]			0				0
Total loans				13,152		14,080		14,670	[3]
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[3]	508	267
Provision charged (credited) to income	[3]	(39)	197
Charge offs	[3]	0	(7)
Recoveries	[3]	1	0
Net (charge offs) recoveries	[3]	1	(7)
Balance at end of period	[3]	470	457
Ending balance: collectively evaluated for impairment	[3]			247				285
Ending balance: individually evaluated for impairment	[3]			223				172
Total allowances for credit losses	[3]	508	267	470		508		457
Collectively evaluated for impairment	[1],[3]			21,974				28,304
Individually evaluated for impairment	[2],[3]			553				297
Loans carried at the lower of amortized cost or fair value less cost to sell	[3]			0				0
Total loans				22,527	[4],[5]	23,481	[4],[5]	28,601	[3]
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		13	19
Provision charged (credited) to income		2	(3)
Charge offs		0	0
Recoveries		0	0
Net (charge offs) recoveries		0	0
Balance at end of period		15	16
Ending balance: collectively evaluated for impairment				14				15
Ending balance: individually evaluated for impairment				1				1
Total allowances for credit losses		13	19	15		13		16
Collectively evaluated for impairment	[1]			3,508				8,164
Individually evaluated for impairment	[2]			7				7
Loans carried at the lower of amortized cost or fair value less cost to sell				0				0
Total loans				3,515	[5]	5,765	[5]	8,171
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans				19,592		19,659
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		26	68
Provision charged (credited) to income		0	(9)
Charge offs		(3)	(9)
Recoveries		1	5
Net (charge offs) recoveries		(2)	(4)
Balance at end of period		24	55
Ending balance: collectively evaluated for impairment				16				25
Ending balance: individually evaluated for impairment				8				30
Total allowances for credit losses		26	68	24		26		55
Collectively evaluated for impairment	[1]			16,181				16,244
Individually evaluated for impairment	[2]			57				191
Loans carried at the lower of amortized cost or fair value less cost to sell				981				1,086
Total loans				17,219		17,181		17,521
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		20	24
Provision charged (credited) to income		(2)	3
Charge offs		(2)	(3)
Recoveries		1	1
Net (charge offs) recoveries		(1)	(2)
Balance at end of period		17	25
Ending balance: collectively evaluated for impairment				16				24
Ending balance: individually evaluated for impairment				1				1
Total allowances for credit losses		20	24	17		20		25
Collectively evaluated for impairment	[1]			1,271				1,467
Individually evaluated for impairment	[2]			4				5
Loans carried at the lower of amortized cost or fair value less cost to sell				69				72
Total loans				1,344		1,408		1,544
Consumer Loans [Member] | Credit Cards [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		34	32
Provision charged (credited) to income		3	5
Charge offs		(8)	(8)
Recoveries		2	2
Net (charge offs) recoveries		(6)	(6)
Balance at end of period		31	31
Ending balance: collectively evaluated for impairment				30				30
Ending balance: individually evaluated for impairment				1				1
Total allowances for credit losses		34	32	31		34		31
Collectively evaluated for impairment	[1]			642				655
Individually evaluated for impairment	[2]			4				5
Loans carried at the lower of amortized cost or fair value less cost to sell				0				0
Total loans				646		688		660
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		7	9
Provision charged (credited) to income		0	2
Charge offs		(1)	(1)
Recoveries		0	0
Net (charge offs) recoveries		(1)	(1)
Balance at end of period		6	10
Ending balance: collectively evaluated for impairment				6				10
Ending balance: individually evaluated for impairment				0				0
Total allowances for credit losses		$ 7	$ 9	6		7		10
Collectively evaluated for impairment	[1]			383				395
Individually evaluated for impairment	[2]			0				0
Loans carried at the lower of amortized cost or fair value less cost to sell				0				0
Total loans				$ 383		$ 382		$ 395

[1] During the first quarter of 2017, in conjunction with the creation of the new Corporate Center segment as discussed further in Note 13, "Business Segments," we reclassified loans to HSBC affiliates from global banking to other commercial and revised the prior period to conform with the current year presentation. As a result, other commercial includes loans to HSBC affiliates totaling $939 million and $5,107 million at March 31, 2017 and 2016, respectively, for which we do not carry an associated allowance for credit losses.

[2] For consumer loans and certain small business loans, these amounts represent TDR Loans for which we evaluate reserves using a discounted cash flow methodology. Each loan is individually identified as a TDR Loan and then grouped together with other TDR Loans with similar characteristics. The discounted cash flow analysis is then applied to these groups of TDR Loans. Loans individually evaluated for impairment exclude TDR Loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell which totaled $681 million and $771 million at March 31, 2017 and 2016, respectively

[3] During the fourth quarter of 2016, we transferred certain client relationships from CMB to GB&M as discussed further in Note 13, "Business Segments." As a result, we reclassified $4.7 billion of loans and $28 million of allowance for credit losses from business and corporate banking to global banking at March 31, 2016 to conform with the current year presentation

[4] Represents large multinational firms including globally focused U.S. corporate and financial institutions, U.S. dollar lending to multinational banking clients managed by HSBC on a global basis and complex large business clients supported by GB&M relationship managers.

[5] Represents large multinational firms including globally focused U.S. corporate and financial institutions, U.S. dollar lending to multinational banking clients managed by HSBC on a global basis and complex large business clients supported by GB&M relationship managers. (2)During the first quarter of 2017, in conjunction with the creation of the new Corporate Center segment as discussed further in Note 13, "Business Segments," we reclassified loans to HSBC affiliates from global banking to other commercial and revised the prior period to conform with the current year presentation. As a result, other commercial includes loans to HSBC affiliates which totaled $939 million and $3,274 million at March 31, 2017 and December 31, 2016, respectively. All tables below have been restated to reflect this reclassification, as applicable. See Note 12, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.