Restatement of Previously Issued Financial Statements (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended	3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended	36 Months Ended		3 Months Ended	12 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2013 As Reported [Member]	Jun. 30, 2013 As Reported [Member]	Mar. 31, 2013 As Reported [Member]	Dec. 31, 2012 As Reported [Member]	Sep. 30, 2012 As Reported [Member]	Jun. 30, 2012 As Reported [Member]	Mar. 31, 2012 As Reported [Member]	Dec. 31, 2011 As Reported [Member]	Sep. 30, 2012 As Reported [Member]	Sep. 30, 2011 As Reported [Member]	Sep. 30, 2012 Cumulative Prior Period Adjustments [Member]	Jun. 30, 2013 FY 2012 Adjustment [Member]	Sep. 30, 2012 FY 2012 Adjustment [Member]	Sep. 30, 2011 FY 2012 Adjustment [Member]	Sep. 30, 2012 FY 2012 Adjustment [Member]	Sep. 30, 2010 FY 2012 Adjustment [Member]	Jun. 30, 2013 As Restated [Member]	Mar. 31, 2013 As Restated [Member]	Dec. 31, 2012 As Restated [Member]	Sep. 30, 2012 As Restated [Member]	Jun. 30, 2012 As Restated [Member]	Mar. 31, 2012 As Restated [Member]	Dec. 31, 2011 As Restated [Member]	Sep. 30, 2012 As Restated [Member]	Sep. 30, 2011 As Restated [Member]
Receivables from Brokers-Dealers and Clearing Organizations	$ 168.3	$ 116.8						$ 127.4				$ 127.4		$ (7.1)		$ (3.5)		$ (3.5)					$ 116.8				$ 116.8
Income taxes receivable	15.5	15.5						11.9				11.9		2.3		1.3		1.3					15.5				15.5
Goodwill and intangible assets, net	59.1	55.8						54.7				54.7		1.1		0		0					55.8				55.8
Assets	2,848.0	2,953.0	2,632.0					2,958.9				2,958.9		(3.7)		(2.2)		(2.2)					2,953.0				2,953.0
Liabilities	2,512.6	2,639.8						2,639.8				2,639.8		0		0		0					2,639.8				2,639.8
Retained earnings	125.4	106.1						112.0				112.0		(3.7)		(2.2)		(2.2)					106.1				106.1
Total stockholders' equity	335.4	313.2						319.1				319.1		(3.7)		(2.2)		(2.2)	1.2				313.2				313.2
Total liabilities and equity	2,848.0	2,953.0						2,958.9				2,958.9		(3.7)		(2.2)		(2.2)					2,953.0				2,953.0
Sales of physical commodities	43,283.7	67,514.7	72,521.2									68,812.5	75,123.4			(1,297.8)	(2,602.2)										67,514.7	72,521.2
Trading gains, net	265.0	244.9	201.6									248.4	205.7			(3.5)	(4.1)										244.9	201.6
Total revenues	43,768.3	67,959.3	72,891.3	9,030.4	11,039.5	13,113.1	12,719.5	17,668.1	17,351.1	16,951.0	17,290.4	69,260.6	75,497.6			(1,301.3)	(2,606.3)			9,996.6	12,188.5	12,552.8	17,369.1	17,192.9	16,808.0	16,589.3	67,959.3	72,891.3
Cost of sales of physical commodities	43,289.9	67,505.1	72,472.2	8,917.8	10,917.4	12,995.8	12,593.8	17,550.1	17,227.3	16,831.4	17,194.1	68,802.9	75,074.4			(1,297.8)	(2,602.2)			9,873.8	12,071.2	12,427.1	17,251.2	17,071.4	16,689.5	16,493.0	67,505.1	72,472.2
Operating revenues	478.4	454.2	419.1	112.6	122.1	117.3	125.7	118.0	123.8	119.6	96.3	457.7	423.2			(3.5)	(4.1)			122.8	117.3	125.7	117.9	121.5	118.5	96.3	454.2	419.1
Net operating revenues	315.3	306.2	308.2	70.2	79.0	76.2	89.2	79.4	83.0	81.1	66.2	309.7	312.3			(3.5)	(4.1)			79.7	76.2	89.2	79.3	80.7	80.0	66.2	306.2	308.2
Income from continuing operations, before tax	22.6	15.8	55.4	(2.5)	4.1	1.4	18.8	10.5	5.9	3.6	(0.7)	19.3	59.5			(3.5)	(4.1)			4.9	1.4	18.8	10.4	3.6	2.5	(0.7)	15.8	55.4
Income tax expense	3.3	3.1	20.9	(3.7)	1.3	(0.1)	5.5	2.2	1.2	1.2	(0.2)	4.4	22.5			(1.3)	(1.6)			1.6	(0.1)	5.5	2.1	0.4	0.8	(0.2)	3.1	20.9
Net income attributable to INTL FCStone Inc. common stockholders	19.3	12.8	34.8					8.3	4.7	2.4	(0.4)	15.0	37.3		0.5	(2.2)	(2.5)	5.9					8.3	3.2	1.7	(0.4)	12.8	34.8
Comprehensive income	$ 15.1	$ 16.5	$ 31.8									$ 18.7	$ 34.3			$ (2.2)	$ (2.5)										$ 16.5	$ 31.8
Net basic earnings per share	$ 1.01	$ 0.67	$ 1.93	$ 0.05	$ 0.15	$ 0.08	$ 0.70	$ 0.44	$ 0.24	$ 0.13	$ (0.02)	$ 0.79	$ 2.07			$ (0.12)	$ (0.14)			$ 0.18	$ 0.08	$ 0.70	$ 0.44	$ 0.16	$ 0.09	$ (0.02)	$ 0.67	$ 1.93
Net diluted earnings per share	$ 0.97	$ 0.64	$ 1.83	$ 0.04	$ 0.15	$ 0.08	$ 0.68	$ 0.42	$ 0.23	$ 0.12	$ (0.02)	$ 0.75	$ 1.96			$ (0.11)	$ (0.13)			$ 0.17	$ 0.08	$ 0.68	$ 0.42	$ 0.15	$ 0.09	$ (0.02)	$ 0.64	$ 1.83

Amount combines the carrying amounts for goodwill and finite- and indefinite-lived intangible assets. Goodwill represents the carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquire, adjusted for any amortization recognized prior to adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions. Indefinite-lived intangible assets represent the carrying amount of intangible assets, excluding goodwill, which have a projected indefinite period of benefit (hence are not amortized), allocated to the reportable segment. These assets, acquired either individually or as part of a group of assets, in either an asset acquisition or business combination, are assessed at least annually for impairment. Examples may include trade secrets, contractual rights, trade names, and licensing agreements. Finite-lived intangible assets are the aggregate sum of gross carrying value of a major finite-lived intangible asset class, less accumulated amortization and any impairment charges. A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company.

No definition available.