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Net segment contribution equals revenues less cost of sales, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense.

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Segment Income equals net contribution less non-variable direct segment costs.

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

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Amount of gain (loss) related to nonoperating activities, classified as other.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income after deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Segment and Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 6,078.8	$ 7,118.3	$ 6,507.0	$ 7,918.6	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 27,622.7	$ 29,423.6	$ 14,754.9
Operating revenues	243.2	259.8	260.2	212.6	205.1	197.6	195.8	185.5	975.8	784.0	671.0
Revenues, Net of Interest Expense	142.4	154.6	154.3	130.3	131.1	123.3	123.9	114.3	581.6	492.6	443.9
Net Segment Contribution									432.4	387.0	347.0
Segment Income									261.9	169.0	206.0
Costs not allocated to operating segments									162.4	153.8	139.5
Other gains									2.0	0.0	6.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	20.5	$ 32.9	$ 29.5	$ 18.6	(22.5)	$ 15.0	$ 14.3	$ 8.4	101.5	15.2	72.7
Assets	7,824.7				6,243.4				7,824.7	6,243.4	5,950.3
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues									286.7	244.6	236.1
Operating revenues									286.7	244.6	236.1
Revenues, Net of Interest Expense									226.4	194.3	188.2
Net Segment Contribution									164.7	141.8	134.4
Segment Income									96.4	72.8	68.7
Assets	1,935.7				1,650.3				1,935.7	1,650.3	1,637.5
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues									99.2	89.2	73.2
Operating revenues									99.2	89.2	73.2
Revenues, Net of Interest Expense									93.5	80.6	65.3
Net Segment Contribution									75.0	64.4	52.2
Segment Income									59.8	50.6	39.8
Assets	206.6				199.5				206.6	199.5	191.4
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues									196.2	151.7	175.2
Operating revenues									196.2	151.7	175.2
Revenues, Net of Interest Expense									94.6	94.6	121.9
Net Segment Contribution									69.1	75.6	97.5
Segment Income									40.8	46.6	69.4
Assets	3,058.2				2,101.7				3,058.2	2,101.7	2,130.7
Physical Commodities Segment [Member]
Segment Reporting Information [Line Items]
Revenues									26,703.8	28,684.4	14,120.5
Operating revenues									56.9	44.8	36.6
Revenues, Net of Interest Expense									44.8	37.3	31.5
Net Segment Contribution									31.8	27.2	23.4
Segment Income									16.6	(31.4)	13.3
Assets	413.7				339.5				413.7	339.5	258.0
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues									332.4	259.8	151.1
Operating revenues									332.4	259.8	151.1
Revenues, Net of Interest Expense									122.6	102.2	48.8
Net Segment Contribution									91.8	78.0	39.5
Segment Income									48.3	30.4	14.8
Assets	2,109.9				1,818.9				2,109.9	1,818.9	1,617.4
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues									4.4	(6.1)	(1.2)
Operating revenues									4.4	(6.1)	(1.2)
Revenues, Net of Interest Expense									(0.3)	(16.4)	(11.8)
Assets	$ 100.6				$ 133.5				$ 100.6	$ 133.5	$ 115.3