Litigation and Regulatory Matters - Additional Information (Details)	1 Months Ended									12 Months Ended		36 Months Ended
	Oct. 31, 2018 USD ($)	Jan. 31, 2018	Oct. 31, 2017 former_employee	Mar. 31, 2017 USD ($)	Feb. 28, 2017 financial_institution	Aug. 31, 2016 former_employee	Nov. 30, 2015 plaintiff count	Sep. 30, 2015 USD ($)	Feb. 28, 2015	Dec. 31, 2018 USD ($)	Dec. 31, 2012 plaintiff county	Dec. 31, 2007 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2014 trust
Loss Contingencies [Line Items]
Expense related to various legal matters										$ 522,000,000
Estimate of reasonably possible loss										350,000,000
Foreign Exchange Market Regulatory Investigation [Member] | HSBC Holdings plc [Member]
Loss Contingencies [Line Items]
Litigation settlement agreement, compliance period		3 years
Number of former employees indicted | former_employee						2
Number of former employees found guilty | former_employee			1
Dekalb County et. al. v. HSBC North America Holdings, Inc. et. al. [Member]
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff											3
Number of counties in the area | county											5
Foreign Exchange Class Action [Member]
Loss Contingencies [Line Items]
Litigation settlement amount								$ 285,000,000
Foreign Exchange Class Action [Member] | HSBC Bank USA [Member]
Loss Contingencies [Line Items]
Litigation settlement amount								$ 14,250,000
Deutsche Bank Alleged Breach of Representation [Member]
Loss Contingencies [Line Items]
Damages sought										508,000,000
Mortgage Securitization Pool Trust Litigation [Member]
Loss Contingencies [Line Items]
Damages sought										38,000,000,000
Number of identified trusts | trust														280
Shareholder Derivative Action [Member]
Loss Contingencies [Line Items]
Deferred Prosecution Agreement, Term									5 years
Jeffrey Siegel, et al. v. HSBC Holdings plc, et al. [Member]
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff							4
Number of counts included in legal complaint | count							1
Roberto Vasquez and Eva Garcia et al v. Hong Kong and Shanghai Banking Corporation, LTD., HSBC Bank USA, N.A., et al. [Member]
Loss Contingencies [Line Items]
Damages sought										37,000,000
Telephone Consumer Protection Act Litigation [Member]
Loss Contingencies [Line Items]
Damages sought, per violation				$ 1,500
South African Competition Tribunal [Member]
Loss Contingencies [Line Items]
Number of financial institutions | financial_institution					18
Mortgage Securitization Activity Related Litigation [Member]
Loss Contingencies [Line Items]
Payments for legal settlements	$ 492,000,000
Mortgage Securitization Activity Related Litigation [Member] | HSBC North America [Member]
Loss Contingencies [Line Items]
Payments for legal settlements	$ 765,000,000
Mortgage Securitization Activity Related Litigation [Member] | HSBC Securities [Member]
Loss Contingencies [Line Items]
Mortgage securitization loan purchased and sold												$ 24,000,000,000
Mortgage securitization outstanding loan purchase and sold										$ 3,800,000,000			$ 4,100,000,000