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, 2016		Mar. 31, 2015	Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 912		$ 680
Provision for credit losses		157		53
Charge offs		(56)	[1]	(38)
Recoveries		10		8
Net (charge offs) recoveries		(46)		(30)
Balance at end of period		1,023		703
Ending balance: collectively evaluated for impairment					$ 734				$ 631
Ending balance: individually evaluated for impairment					289				72
Total allowances for credit losses		912		680	1,023		$ 912		703
Collectively evaluated for impairment	[2]				79,660				79,351
Individually evaluated for impairment	[3]				914				543
Loans carried at the lower of amortized cost or fair value less cost to sell					1,158				1,564
Total loans					81,732		82,917		81,458
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans					61,612		62,453
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		86		89
Provision for credit losses		9		2
Charge offs		0	[1]	(1)
Recoveries		0		0
Net (charge offs) recoveries		0		(1)
Balance at end of period		95		90
Ending balance: collectively evaluated for impairment					94				87
Ending balance: individually evaluated for impairment					1				3
Total allowances for credit losses		86		89	95		86		90
Collectively evaluated for impairment	[2]				10,067				10,702
Individually evaluated for impairment	[3]				103				199
Loans carried at the lower of amortized cost or fair value less cost to sell					0				0
Total loans					10,170		10,000		10,901
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		434		275
Provision for credit losses		(46)		24
Charge offs		(28)	[1]	(6)
Recoveries		2		2
Net (charge offs) recoveries		(26)		(4)
Balance at end of period		362		295
Ending balance: collectively evaluated for impairment					279				272
Ending balance: individually evaluated for impairment					83				23
Total allowances for credit losses		434		275	362		434		295
Collectively evaluated for impairment	[2]				19,059				19,155
Individually evaluated for impairment	[3]				353				96
Loans carried at the lower of amortized cost or fair value less cost to sell					0				0
Total loans					19,412		19,116		19,251
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		240		107
Provision for credit losses		196		21
Charge offs		(7)	[1]	0
Recoveries		0		0
Net (charge offs) recoveries		(7)		0
Balance at end of period		429		128
Ending balance: collectively evaluated for impairment					257				128
Ending balance: individually evaluated for impairment					172				0
Total allowances for credit losses		240		107	429		240		128
Collectively evaluated for impairment	[2]				28,716				28,016
Individually evaluated for impairment	[3]				250				13
Loans carried at the lower of amortized cost or fair value less cost to sell					0				0
Total loans					28,966	[4]	29,969	[4]	28,029
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		19		21
Provision for credit losses		(3)		1
Charge offs		0	[1]	(1)
Recoveries		0		0
Net (charge offs) recoveries		0		(1)
Balance at end of period		16		21
Ending balance: collectively evaluated for impairment					15				20
Ending balance: individually evaluated for impairment					1				1
Total allowances for credit losses		19		21	16		19		21
Collectively evaluated for impairment	[2]				3,057				3,459
Individually evaluated for impairment	[3]				7				7
Loans carried at the lower of amortized cost or fair value less cost to sell					0				0
Total loans					3,064		3,368		3,466
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans					20,120		20,464
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		68		107
Provision for credit losses		(9)		0
Charge offs		(9)	[1]	(14)
Recoveries		5		2
Net (charge offs) recoveries		(4)		(12)
Balance at end of period		55		95
Ending balance: collectively evaluated for impairment					25				53
Ending balance: individually evaluated for impairment					30				42
Total allowances for credit losses		68		107	55		68		95
Collectively evaluated for impairment	[2]				16,244				15,281
Individually evaluated for impairment	[3]				191				217
Loans carried at the lower of amortized cost or fair value less cost to sell					1,086				1,493
Total loans					17,521	[5],[6]	17,758		16,991
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		24		32
Provision for credit losses		3		(2)
Charge offs		(3)	[1]	(2)
Recoveries		1		1
Net (charge offs) recoveries		(2)		(1)
Balance at end of period		25		29
Ending balance: collectively evaluated for impairment					24				28
Ending balance: individually evaluated for impairment					1				1
Total allowances for credit losses		24		32	25		24		29
Collectively evaluated for impairment	[2]				1,467				1,640
Individually evaluated for impairment	[3]				5				5
Loans carried at the lower of amortized cost or fair value less cost to sell					72				71
Total loans					1,544		1,600		1,716
Consumer Loans [Member] | Credit Cards [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		32		39
Provision for credit losses		5		3
Charge offs		(8)	[1]	(8)
Recoveries		2		1
Net (charge offs) recoveries		(6)		(7)
Balance at end of period		31		35
Ending balance: collectively evaluated for impairment					30				33
Ending balance: individually evaluated for impairment					1				2
Total allowances for credit losses		32		39	31		32		35
Collectively evaluated for impairment	[2]				655				674
Individually evaluated for impairment	[3]				5				6
Loans carried at the lower of amortized cost or fair value less cost to sell					0				0
Total loans					660		699		680
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		9		10
Provision for credit losses		2		4
Charge offs		(1)	[1]	(6)
Recoveries		0		2
Net (charge offs) recoveries		(1)		(4)
Balance at end of period		10		10
Ending balance: collectively evaluated for impairment					10				10
Ending balance: individually evaluated for impairment					0				0
Total allowances for credit losses		$ 9		$ 10	10		9		10
Collectively evaluated for impairment	[2]				395				424
Individually evaluated for impairment	[3]				0				0
Loans carried at the lower of amortized cost or fair value less cost to sell					0				0
Total loans					$ 395		$ 407		$ 424

[1] 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 months ended March 31, 2016 and, accordingly, we recognized the existing allowance for credit losses on these loans as additional charge-off totaling $2 million during the three months ended March 31, 2016.

[2] Global Banking includes loans to HSBC affiliates totaling $5,107 million and $5,016 million at March 31, 2016 and 2015, respectively, for which we do not carry an associated allowance for credit losses.

[3] 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 $771 million and $778 million at March 31, 2016 and 2015, respectively.

[4] 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 $5,107 million and $4,815 million at March 31, 2016 and December 31, 2015, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.

[5] The decrease in nonaccrual loans at March 31, 2016 reflects the impact of the transfer of certain residential mortgage loans with a carrying value of $345 million to held for sale during the first quarter of 2016.

[6] The decrease in past due loans at March 31, 2016 reflects the impact of the transfer of certain residential mortgage loans with a carrying value of $345 million to held for sale during the first quarter of 2016. See Note 6, "Loans Held for Sale," for additional details.