Litigation and Regulatory Matters - Additional Information (Details) $ in Thousands	1 Months Ended												12 Months Ended						36 Months Ended
	Dec. 31, 2019 USD ($)	Oct. 28, 2019 USD ($)	Sep. 30, 2019 CAD ($)	Feb. 28, 2019 USD ($) trust	Mar. 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	Feb. 28, 2015	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2014 USD ($) trust	Dec. 31, 2013 USD ($)	Dec. 31, 2012 plaintiff county	Dec. 31, 2007 USD ($)
Loss Contingencies [Line Items]
Expense related to various legal matters													$ 54,000,000	$ 522,000,000	$ 29,000,000
Estimate of reasonably possible loss	$ 225,000,000												225,000,000
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
Litigation settlement	580,000
County of Cook v. HSBC North America Holdings Inc., et. al. [Member]
Loss Contingencies [Line Items]
Litigation settlement	580,000
Supranational, Sovereign and Agency Bonds [Member]
Loss Contingencies [Line Items]
Litigation settlement			$ 1,323
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
Rigoberto 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
HSBC Bank USA [Member] | Commodity Futures Trading Commission Investigation [Member]
Loss Contingencies [Line Items]
Civil monetary penalty paid		$ 650,000
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
HSBC Securities [Member] | Mortgage Securitization Activity Related Litigation [Member]
Loss Contingencies [Line Items]
Mortgage securitization loan purchased and sold																			$ 24,000,000,000
Mortgage securitization outstanding loan purchase and sold	$ 3,400,000,000												$ 3,400,000,000	$ 3,800,000,000
Park Royal LLC [Member] | Mortgage Securitization Pool Trust Litigation [Member]
Loss Contingencies [Line Items]
Damages sought				$ 59,000,000
Number of identified trusts | trust				3