DEI - shares	9 Months Ended
	Jun. 30, 2019	Aug. 06, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	INTL FCSTONE INC.
Trading Symbol	INTL
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	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		19,163,763
Entity Small Business Submission type	false
Entity Emerging Growth Company submission type	false
Entity Current Reporting Status	Yes