DEI - shares	3 Months Ended
	Dec. 31, 2019	Feb. 03, 2020
Document and Entity Information [Abstract]
Entity Registrant Name	INTL FCSTONE INC.
Entity Central Index Key	0000913760
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		19,301,552
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Interactive Data Current	Yes