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			9 Months Ended
		Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2016		Dec. 31, 2015		Sep. 30, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 1,063		$ 648	$ 912		$ 680
Provision charged (credited) to income		62	[1]	47	353	[1]	94
Charge offs		(79)	[1],[2]	(24)	(238)	[1],[2]	(126)
Recoveries		14		7	33		30
Net (charge offs) recoveries		(65)		(17)	(205)		(96)
Balance at end of period		1,060		678	1,060		678
Ending balance: collectively evaluated for impairment								$ 706				$ 623
Ending balance: individually evaluated for impairment								354				55
Total allowances for credit losses		1,063		648	912		680	1,060		$ 912		678
Collectively evaluated for impairment	[3]							75,439				82,868
Individually evaluated for impairment	[4]							1,206				556
Loans carried at the lower of amortized cost or fair value less cost to sell								980				1,518
Total loans								77,625		82,917		84,942
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans								58,032		62,453
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		92		89	86		89
Provision charged (credited) to income		(8)	[1]	(3)	(2)	[1]	(4)
Charge offs		0	[1],[2]	0	0	[1],[2]	(2)
Recoveries		6		1	6		4
Net (charge offs) recoveries		6		1	6		2
Balance at end of period		90		87	90		87
Ending balance: collectively evaluated for impairment								88				86
Ending balance: individually evaluated for impairment								2				1
Total allowances for credit losses		92		89	86		89	90		86		87
Collectively evaluated for impairment	[3]							10,899				11,980
Individually evaluated for impairment	[4]							59				116
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								10,958		10,000		12,096
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		358		260	434		275
Provision charged (credited) to income		7	[1]	32	(35)	[1]	54
Charge offs		(26)	[1],[2]	(11)	(65)	[1],[2]	(55)
Recoveries		3		2	8		9
Net (charge offs) recoveries		(23)		(9)	(57)		(46)
Balance at end of period		342		283	342		283
Ending balance: collectively evaluated for impairment								274				269
Ending balance: individually evaluated for impairment								68				14
Total allowances for credit losses		358		260	434		275	342		434		283
Collectively evaluated for impairment	[3]							17,218				19,325
Individually evaluated for impairment	[4]							447				189
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								17,665		19,116		19,514
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		488		130	240		107
Provision charged (credited) to income		44	[1]	16	377	[1]	39
Charge offs		(7)	[1],[2]	0	(92)	[1],[2]	0
Recoveries		0		0	0		0
Net (charge offs) recoveries		(7)		0	(92)		0
Balance at end of period		525		146	525		146
Ending balance: collectively evaluated for impairment								254				146
Ending balance: individually evaluated for impairment								271				0
Total allowances for credit losses		488		130	240		107	525		240		146
Collectively evaluated for impairment	[3]							25,792				29,787
Individually evaluated for impairment	[4]							622				21
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								26,414	[5]	29,969	[5]	29,808
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		15		18	19		21
Provision charged (credited) to income		(1)	[1]	(1)	(5)	[1]	(3)
Charge offs		0	[1],[2]	0	0	[1],[2]	(1)
Recoveries		0		0	0		0
Net (charge offs) recoveries		0		0	0		(1)
Balance at end of period		14		17	14		17
Ending balance: collectively evaluated for impairment								13				17
Ending balance: individually evaluated for impairment								1				0
Total allowances for credit losses		15		18	19		21	14		19		17
Collectively evaluated for impairment	[3]							2,988				3,328
Individually evaluated for impairment	[4]							7				6
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								2,995		3,368		3,334
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans								19,593		20,464
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		50		83	68		107
Provision charged (credited) to income		11	[1]	(3)	(5)	[1]	(9)
Charge offs		(34)	[1],[2]	(3)	(43)	[1],[2]	(27)
Recoveries		3		2	10		8
Net (charge offs) recoveries		(31)		(1)	(33)		(19)
Balance at end of period		30		79	30		79
Ending balance: collectively evaluated for impairment								20				41
Ending balance: individually evaluated for impairment								10				38
Total allowances for credit losses		50		83	68		107	30		68		79
Collectively evaluated for impairment	[3]							16,121				15,801
Individually evaluated for impairment	[4]							62				214
Loans carried at the lower of amortized cost or fair value less cost to sell								908				1,445
Total loans								17,091	[6],[7]	17,758		17,460
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		19		27	24		32
Provision charged (credited) to income		1	[1]	(2)	(2)	[1]	(4)
Charge offs		(4)	[1],[2]	(1)	(9)	[1],[2]	(6)
Recoveries		1		1	4		3
Net (charge offs) recoveries		(3)		0	(5)		(3)
Balance at end of period		17		25	17		25
Ending balance: collectively evaluated for impairment								16				24
Ending balance: individually evaluated for impairment								1				1
Total allowances for credit losses		19		27	24		32	17		24		25
Collectively evaluated for impairment	[3]							1,378				1,561
Individually evaluated for impairment	[4]							4				5
Loans carried at the lower of amortized cost or fair value less cost to sell								72				73
Total loans								1,454		1,600		1,639
Consumer Loans [Member] | Credit Cards [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		33		33	32		39
Provision charged (credited) to income		7	[1]	7	21	[1]	14
Charge offs		(7)	[1],[2]	(8)	(23)	[1],[2]	(24)
Recoveries		1		1	4		4
Net (charge offs) recoveries		(6)		(7)	(19)		(20)
Balance at end of period		34		33	34		33
Ending balance: collectively evaluated for impairment								33				32
Ending balance: individually evaluated for impairment								1				1
Total allowances for credit losses		33		33	32		39	34		32		33
Collectively evaluated for impairment	[3]							663				677
Individually evaluated for impairment	[4]							5				5
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								668		699		682
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		8		8	9		10
Provision charged (credited) to income		1	[1]	1	4	[1]	7
Charge offs		(1)	[1],[2]	(1)	(6)	[1],[2]	(11)
Recoveries		0		0	1		2
Net (charge offs) recoveries		(1)		(1)	(5)		(9)
Balance at end of period		8		8	8		8
Ending balance: collectively evaluated for impairment								8				8
Ending balance: individually evaluated for impairment								0				0
Total allowances for credit losses		$ 8		$ 8	$ 9		$ 10	8		9		8
Collectively evaluated for impairment	[3]							380				409
Individually evaluated for impairment	[4]							0				0
Loans carried at the lower of amortized cost or fair value less cost to sell								0				0
Total loans								$ 380		$ 407		$ 409

[1] The provision for credit losses and charge-offs for residential mortgage loans during both the three and nine months ended September 30, 2016 includes $11 million related to the lower of amortized cost or fair value adjustment attributable to credit factors for loans transferred to held for sale. See Note 6, "Loans Held for Sale," for additional information.

[2] For collateral dependent loans that are transferred to held for sale, the existing allowance for credit losses at the time of transfer are recognized as a charge-off. We transferred to held for sale certain residential mortgage loans during the three and nine months ended September 30, 2016 and, accordingly, we recognized the existing allowance for credit losses on these loans as additional charge-off totaling $20 million and $22 million during the three and nine months ended September 30, 2016, respectively.

[3] Global Banking includes loans to HSBC affiliates totaling $4,463 million and $5,447 million at September 30, 2016 and 2015, respectively, for which we do not carry an associated allowance for credit losses.

[4] 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 $662 million and $858 million at September 30, 2016 and 2015, respectively.

[5] Represents large multinational firms including globally focused U.S. corporate and financial institutions and U.S. dollar lending to multinational banking customers managed by HSBC on a global basis. Also includes loans to HSBC affiliates which totaled $4,463 million and $4,815 million at September 30, 2016 and December 31, 2015, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.

[6] The decrease in nonaccrual loans at September 30, 2016 reflects the impact of transfers of certain residential mortgage loans to held for sale during the nine months ended September 30, 2016.

[7] The decrease in past due loans at September 30, 2016 reflects the impact of transfers of certain residential mortgage loans to held for sale during the nine months ended September 30, 2016. See Note 6, "Loans Held for Sale" for additional details.