Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Derivative, notional amount	$ 4,542,542,000,000		$ 4,542,542,000,000			$ 4,829,655,000,000
HSBC North America Inc. HNAI [Member]
Related Party Transaction [Line Items]
Maximum borrowing capacity	150,000,000		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, Related Parties	3,014,000,000		3,014,000,000			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
Loan And Lease Receivable Revolving Line Of Credit Outstanding	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
Loan And Lease Receivable Revolving Line Of Credit Outstanding	0		0			0
HMUS [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	10,700,000,000		10,700,000,000			6,700,000,000
Loans and Leases Receivable, Related Parties	506,000,000		506,000,000			563,000,000
Loan And Lease Receivable Revolving Line Of Credit Outstanding	506,000,000		506,000,000			563,000,000
HSBC Bank Brasil [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	1,200,000,000		1,200,000,000			1,200,000,000
Loans and Leases Receivable, Related Parties	1,102,000,000		1,102,000,000			1,108,000,000
Loan And Lease Receivable Revolving Line Of Credit Outstanding	1,100,000,000		1,100,000,000			1,100,000,000
HSBC Mexico [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	1,200,000,000		1,200,000,000			1,200,000,000
Loans and Leases Receivable, Related Parties	725,000,000		725,000,000			75,000,000
Other Affiliates [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	2,100,000,000		2,100,000,000			2,100,000,000
Loans and Leases Receivable, Related Parties	100,000,000		100,000,000			61,000,000
Loan And Lease Receivable Revolving Line Of Credit Outstanding	0		0			0
Regency [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Liquidity Facility, Notional Amount	3,100,000,000		3,100,000,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Loans and Leases Receivable, Related Parties	5,447,000,000		5,447,000,000			4,821,000,000
Derivative, notional amount	1,011,400,000,000		1,011,400,000,000			1,082,600,000,000
Fair value of derivative assets and liabilities	142,000,000		142,000,000			1,166,000,000
Floating Rate Notes [Member] | Hnah [Member] | Senior debt [Member]
Related Party Transaction [Line Items]
Debt issued	1,000,000,000		1,000,000,000			4,000,000,000
Floating Rate Notes [Member] | Hnah [Member] | Subordinated Debt [Member]
Related Party Transaction [Line Items]
Debt issued	850,000,000		850,000,000		$ 850,000,000
Residential Mortgage [Member] | HSBC Finance Corporation [Member]
Related Party Transaction [Line Items]
Carrying Amount At Period End of Residential Mortgage Loans Serviced By HSBC Finance	731,000,000		731,000,000			$ 837,000,000
Support Services From Affiliates [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Rent from related party	$ 15,000,000	$ 14,000,000	$ 44,000,000	$ 41,000,000