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		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016		Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 921	$ 1,023	$ 1,017		$ 912
Provision charged (credited) to income		(21)	134	(98)		291
Charge offs		(61)	(103)	(97)		(159)
Recoveries		9	9	26		19
Net (charge offs) recoveries		(52)	(94)	(71)		(140)
Balance at end of period		848	1,063	848		1,063
Ending balance: collectively evaluated for impairment								$ 590				$ 680
Ending balance: individually evaluated for impairment								258				383
Total allowances for credit losses		921	1,023	1,017		912		848		$ 1,017		1,063
Collectively evaluated for impairment	[1]							66,050				77,233
Individually evaluated for impairment	[2]							999				1,448
Loans carried at the lower of amortized cost or fair value less cost to sell								1,014				1,129
Total loans								68,063		73,875		79,810
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans								48,588		54,216
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		92	95	92		86
Provision charged (credited) to income		(9)	(3)	(8)		6
Charge offs		(2)	0	(3)		0
Recoveries		0	0	0		0
Net (charge offs) recoveries		(2)	0	(3)		0
Balance at end of period		81	92	81		92
Ending balance: collectively evaluated for impairment								74				90
Ending balance: individually evaluated for impairment								7				2
Total allowances for credit losses		92	95	92		86		81		92		92
Collectively evaluated for impairment	[1]							10,197				10,875
Individually evaluated for impairment	[2]							43				98
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								10,240		10,890		10,973
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		266	334	317	[3]	407	[3]
Provision charged (credited) to income		(5)	5	(47)	[3]	(42)	[3]
Charge offs		(2)	(11)	(23)	[3]	(39)	[3]
Recoveries		2	3	14	[3]	5	[3]
Net (charge offs) recoveries		0	(8)	(9)	[3]	(34)	[3]
Balance at end of period	[3]	261	331	261		331
Ending balance: collectively evaluated for impairment	[3]							221				228
Ending balance: individually evaluated for impairment	[3]							40				103
Total allowances for credit losses		266	334	317	[3]	407	[3]	261	[3]	317	[3]	331	[3]
Collectively evaluated for impairment	[1],[3]							12,584				14,180
Individually evaluated for impairment	[2],[3]							284				456
Loans carried at the lower of amortized cost or fair value less cost to sell	[3]							0				0
Total loans								12,868		14,080		14,636	[3]
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		470	457	508	[3]	267	[3]
Provision charged (credited) to income		0	136	(39)	[3]	333	[3]
Charge offs		(45)	(78)	(45)	[3]	(85)	[3]
Recoveries		0	0	1	[3]	0	[3]
Net (charge offs) recoveries		(45)	(78)	(44)	[3]	(85)	[3]
Balance at end of period	[3]	425	515	425		515
Ending balance: collectively evaluated for impairment	[3]							223				268
Ending balance: individually evaluated for impairment	[3]							202				247
Total allowances for credit losses		470	457	508	[3]	267	[3]	425	[3]	508	[3]	515	[3]
Collectively evaluated for impairment	[1],[3]							20,446				25,036
Individually evaluated for impairment	[2],[3]							601				688
Loans carried at the lower of amortized cost or fair value less cost to sell	[3]							0				0
Total loans								21,047	[4],[5]	23,481	[4],[5]	25,724	[3]
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		15	16	13		19
Provision charged (credited) to income		0	(1)	2		(4)
Charge offs		(1)	0	(1)		0
Recoveries		0	0	0		0
Net (charge offs) recoveries		(1)	0	(1)		0
Balance at end of period		14	15	14		15
Ending balance: collectively evaluated for impairment								14				14
Ending balance: individually evaluated for impairment								0				1
Total allowances for credit losses		15	16	13		19		14		13		15
Collectively evaluated for impairment	[1]							4,427				8,202
Individually evaluated for impairment	[2]							6				8
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								4,433	[5]	5,765	[5]	8,210
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans								19,475		19,659
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		24	55	26		68
Provision charged (credited) to income		(8)	(7)	(8)		(16)
Charge offs		0	0	(3)		(9)
Recoveries		4	2	5		7
Net (charge offs) recoveries		4	2	2		(2)
Balance at end of period		20	50	20		50
Ending balance: collectively evaluated for impairment								13				22
Ending balance: individually evaluated for impairment								7				28
Total allowances for credit losses		24	55	26		68		20		26		50
Collectively evaluated for impairment	[1]							16,114				16,423
Individually evaluated for impairment	[2]							58				188
Loans carried at the lower of amortized cost or fair value less cost to sell								947				1,056
Total loans								17,119		17,181		17,667
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		17	25	20		24
Provision charged (credited) to income		(4)	(6)	(6)		(3)
Charge offs		(2)	(2)	(4)		(5)
Recoveries		1	2	2		3
Net (charge offs) recoveries		(1)	0	(2)		(2)
Balance at end of period		12	19	12		19
Ending balance: collectively evaluated for impairment								11				18
Ending balance: individually evaluated for impairment								1				1
Total allowances for credit losses		17	25	20		24		12		20		19
Collectively evaluated for impairment	[1]							1,215				1,433
Individually evaluated for impairment	[2]							3				5
Loans carried at the lower of amortized cost or fair value less cost to sell								67				73
Total loans								1,285		1,408		1,511
Consumer Loans [Member] | Credit Cards [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		31	31	34		32
Provision charged (credited) to income		6	9	9		14
Charge offs		(8)	(8)	(16)		(16)
Recoveries		1	1	3		3
Net (charge offs) recoveries		(7)	(7)	(13)		(13)
Balance at end of period		30	33	30		33
Ending balance: collectively evaluated for impairment								29				32
Ending balance: individually evaluated for impairment								1				1
Total allowances for credit losses		31	31	34		32		30		34		33
Collectively evaluated for impairment	[1]							643				663
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								647		688		668
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		6	10	7		9
Provision charged (credited) to income		(1)	1	(1)		3
Charge offs		(1)	(4)	(2)		(5)
Recoveries		1	1	1		1
Net (charge offs) recoveries		0	(3)	(1)		(4)
Balance at end of period		5	8	5		8
Ending balance: collectively evaluated for impairment								5				8
Ending balance: individually evaluated for impairment								0				0
Total allowances for credit losses		$ 6	$ 10	$ 7		$ 9		5		7		8
Collectively evaluated for impairment	[1]							424				421
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								$ 424		$ 382		$ 421

[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 $1,423 million and $5,072 million at June 30, 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 $670 million and $763 million at June 30, 2017 and 2016, respectively

[3] During the fourth quarter of 2016, we transferred certain client relationships from Commercial Banking to Global Banking and Markets as discussed further in Note 13, "Business Segments." As a result, we reclassified $4.4 billion of loans and $27 million of allowance for credit losses from business and corporate banking to global banking at June 30, 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 Global Banking and Markets 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 Global Banking and Markets 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 $1,423 million and $3,274 million at June 30, 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.