Cover Document - shares	9 Months Ended
	Jun. 30, 2020	Aug. 03, 2020
Cover [Abstract]
Entity Information, Former Legal or Registered Name	INTL FCStone Inc.
Title of 12(b) Security	Common Stock, $0.01 par value
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Quarterly Report	true
Document Type	10-Q
Document Period End Date	Jun. 30, 2020
Entity File Number	000-23554
Entity Registrant Name	StoneX Group Inc.
Entity Address, Address Line One	155 East 44th Street
Entity Address, Address Line Two	Suite 900
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10017
City Area Code	(212)
Local Phone Number	485-3500
Entity Tax Identification Number	59-2921318
Trading Symbol	SNEX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		19,368,297
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Central Index Key	0000913760
Current Fiscal Year End Date	--09-30
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3