Litigation and Regulatory Matters - Additional Information (Details) CAD in Millions	1 Months Ended										12 Months Ended				36 Months Ended
	Jan. 31, 2018 transaction	Oct. 31, 2017 former_employee	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Feb. 28, 2017 financial_institution	Aug. 31, 2016 former_employee	Nov. 30, 2015 USD ($) plaintiff count	Sep. 30, 2015 USD ($) complaint	May 31, 2015 USD ($) plaintiff	Nov. 30, 2013 USD ($)	Dec. 31, 2017 USD ($) financial_institution	Dec. 31, 2017 CAD financial_institution	Dec. 31, 2013 mortgage_loan mortgage_servicer	Dec. 31, 2012 USD ($) plaintiff county	Dec. 31, 2007 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2014 trust	Feb. 29, 2012 state mortgage_servicer
Loss Contingencies [Line Items]
Estimate of loss											$ 275,000,000
Deutsche Bank Alleged Breach of Representation [Member]
Loss Contingencies [Line Items]
Damages sought										$ 508,000,000
Foreclosure Practices [Member]
Loss Contingencies [Line Items]
Number of mortgage servicers | mortgage_servicer													12
AML BSA Related Litigation [Member]
Loss Contingencies [Line Items]
Litigation settlement agreement, compliance period														5 years
DeKalb County, et al. v. HSBC North America Holdings Inc., et al. [Member]
Loss Contingencies [Line Items]
Number of plaintiffs injured or killed in 2005 terrorist attack | 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				CAD 15.5
Number of putative class action complaints | complaint								2
South African Competition Tribunal [Member]
Loss Contingencies [Line Items]
Number of financial institutions included in complaint | financial_institution					18
Hau Yin To v. HSBC Bank plc, et al. [Member]
Loss Contingencies [Line Items]
Number of putative class action complaints | plaintiff									2
Damages sought									$ 8,000,000
FIRREA and Other Mortgage-backed Securities Matters [Member]
Loss Contingencies [Line Items]
Number of non-HSBC financial institutions sued by the Department of Justice | financial_institution											1	1
Number of non-HSBC financial institutions with resolved Department of Justice investigations | financial_institution											8	8
Residential Funding Litigation [Member]
Loss Contingencies [Line Items]
Number of mortgage loans | mortgage_loan													8,800
Mortgage Securitization Pool Trust Litigation [Member]
Loss Contingencies [Line Items]
Damages sought											$ 38,000,000,000
Number of identified trusts | trust																	280
Jeffrey Siegel, et al. v. HSBC Holdings plc, et al. [Member]
Loss Contingencies [Line Items]
Number of plaintiffs injured or killed in 2005 terrorist attack | plaintiff							4
Number of counts agains HSBC defendants for violation of the ATA's civil provision | count							1
Ramiro Giron, et al. v. Hong Kong and Shanghai Bank Company, et al. [Member]
Loss Contingencies [Line Items]
Alleged bank transfers							$ 37,000,000
Telephone Consumer Protection Act Litigation [Member]
Loss Contingencies [Line Items]
Damages sought, per violation				$ 1,500
HSBC Bank USA [Member] | Foreclosure Practices [Member]
Loss Contingencies [Line Items]
Number of states under different departments | state																		49
Number of largest domestic mortgage servicers | mortgage_servicer																		5
HSBC Bank USA [Member] | AML BSA Related Litigation [Member]
Loss Contingencies [Line Items]
Payments for legal settlements														$ 1,381,000,000
HSBC Bank USA [Member] | Foreign Exchange Class Action [Member]
Loss Contingencies [Line Items]
Litigation settlement amount								$ 14,250,000
HSBC Bank USA [Member] | Benchmark Rate Litigation [Member]
Loss Contingencies [Line Items]
Litigation settlement amount			$ 14,000,000
HSBC [Member] | Foreign Exchange Market Regulatory Investigation [Member]
Loss Contingencies [Line Items]
Number of former employees indicted | former_employee						2
Number of former employees convicted | former_employee		1
HSBC [Member] | AML BSA Related Litigation [Member]
Loss Contingencies [Line Items]
Payments for legal settlements														$ 1,921,000,000
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											$ 4,100,000,000					$ 4,600,000,000
Consumer Relief [Member] | HSBC Bank USA [Member] | Foreclosure Practices [Member]
Loss Contingencies [Line Items]
Litigation settlement amount				$ 370,000,000
Subsequent Event [Member] | HSBC [Member] | Foreign Exchange Market Regulatory Investigation [Member]
Loss Contingencies [Line Items]
Number of transactions included in fraudulent conduct investigation | transaction	2
Litigation settlement agreement, compliance period	3 years