Related Party Transactions - Additional Information (Details) - USD ($)		3 Months Ended			9 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Jun. 30, 2015
Related Party Transaction [Line Items]
Long-term debt (includes $10.0 billion and $9.2 billion designated under fair value option at September 30, 2016 and December 31, 2015, respectively)		$ 39,500,000,000			$ 39,500,000,000		$ 33,509,000,000
Derivative, notional amount		4,361,069,000,000			4,361,069,000,000		4,212,040,000,000
Hnah [Member]
Related Party Transaction [Line Items]
Long-term debt (includes $10.0 billion and $9.2 billion designated under fair value option at September 30, 2016 and December 31, 2015, respectively)		5,900,000,000			5,900,000,000		1,900,000,000
HSBC North America Inc. HNAI [Member]
Related Party Transaction [Line Items]
Maximum borrowing capacity		150,000,000			150,000,000
Amount outstanding under the loan agreement		0			0		0
HSBC Finance Corporation [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties		3,013,000,000			3,013,000,000		3,014,000,000
HSBC Finance Corporation [Member] | Extended Uncommitted Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit		5,000,000,000.0			$ 5,000,000,000.0		5,000,000,000.0
Debt term					364 days
Maximum maturity for borrowings under uncommitted revolving credit agreement					5 years
Amount outstanding on line of credit		3,000,000,000			$ 3,000,000,000		3,000,000,000
Credit agreement, amount maturing September 2017		500,000,000			500,000,000
Credit agreement amount maturing January 2018		1,500,000,000			1,500,000,000
Credit agreement amount maturing September 2018		1,000,000,000			1,000,000,000
HSBC Finance Corporation [Member] | Extended committed revolving credit facility [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit		1,000,000,000			1,000,000,000		1,000,000,000
Amount outstanding on line of credit		0			0		0
HMUS [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties		473,000,000			473,000,000		978,000,000
Extended loans and lines of credit		8,900,000,000			8,900,000,000		10,700,000,000
Amount outstanding on line of credit		473,000,000			473,000,000		978,000,000
HSBC Mexico [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties		975,000,000			975,000,000		725,000,000
Extended loans and lines of credit		1,200,000,000			1,200,000,000		1,200,000,000
Other Affiliates [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties		2,000,000			2,000,000		40,000,000
Extended loans and lines of credit		3,100,000,000			3,100,000,000
Amount outstanding on line of credit		0			0		0
Regency [Member]
Related Party Transaction [Line Items]
Loans and leases receivable from related parties	[1]	0			0		58,000,000
Notional amount of liquidity facilities							3,400,000,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Long-term debt (includes $10.0 billion and $9.2 billion designated under fair value option at September 30, 2016 and December 31, 2015, respectively)		5,832,000,000			5,832,000,000		1,827,000,000
Loans and leases receivable from related parties		4,463,000,000			4,463,000,000		4,815,000,000
Derivative, notional amount		979,100,000,000			979,100,000,000		1,004,100,000,000
Fair value of derivative assets and liabilities		6,000,000			6,000,000		216,000,000
Floating Rate Note Maturing December 2016 [Member] | Hnah [Member] | Senior debt [Member]
Related Party Transaction [Line Items]
Debt issued								$ 1,000,000,000
Floating Rate Note Maturing August 2021 [Member] | Hnah [Member] | Senior debt [Member]
Related Party Transaction [Line Items]
Debt issued		2,000,000,000			2,000,000,000
Floating Rate Note Maturing May 2025 [Member] | Hnah [Member] | Subordinated Debt [Member]
Related Party Transaction [Line Items]
Debt issued								$ 900,000,000
Floating Rate Note Maturing August 2026 [Member] | Hnah [Member] | Senior debt [Member]
Related Party Transaction [Line Items]
Debt issued		2,000,000,000			2,000,000,000
Residential Mortgage [Member] | HSBC Finance Corporation [Member]
Related Party Transaction [Line Items]
Carrying amount of residential mortgage loans		586,000,000			586,000,000		$ 696,000,000
Support Services From Affiliates [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Rent from related party		$ 16,000,000		$ 15,000,000	$ 47,000,000	$ 44,000,000
6.0 %, Non-Cumulative Series I Preferred Stock [Member] | Hnah [Member]
Related Party Transaction [Line Items]
HSBC USA preferred stock issued			$ 1,265,000,000
HSBC USA preferred stock dividend rate (percent)			6.00%

[1] An asset-backed commercial paper conduit consolidated by an HSBC affiliate.