Segment Analysis (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues	$ 3,399.9	$ 13,627.7
Operating revenues	151.3	137.5
Net operating revenues	102.7	93.2
Net Segment Contribution	85.5	69.9
Segment Income	51.4	40.9
Costs not allocated to operating segments	39.3	27.3
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	12.1	13.6
Assets	5,217.3		$ 5,070.0
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues	55.4	68.4
Operating revenues	55.4	68.4
Net operating revenues	44.3	57.0
Net Segment Contribution	31.7	40.6
Segment Income	15.0	24.9
Assets	1,512.4		1,548.1
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues	18.3	15.2
Operating revenues	18.3	15.2
Net operating revenues	16.3	13.5
Net Segment Contribution	13.0	10.8
Segment Income	10.0	8.2
Assets	120.5		207.3
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	48.8	17.2
Operating revenues	48.8	17.2
Net operating revenues	36.0	10.0
Net Segment Contribution	29.5	6.6
Segment Income	21.9	1.7
Assets	1,949.1		1,861.0
Physical Commodities [Member]
Segment Reporting Information [Line Items]
Revenues	3,254.5	13,496.7
Operating revenues	5.9	6.5
Net operating revenues	4.7	5.6
Net Segment Contribution	3.4	4.4
Segment Income	1.0	2.5
Assets	289.0		190.9
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	29.8	31.2
Operating revenues	29.8	31.2
Net operating revenues	10.4	9.5
Net Segment Contribution	7.9	7.5
Segment Income	3.5	3.6
Assets	1,254.4		1,163.8
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	(6.9)	(1.0)
Operating revenues	(6.9)	(1.0)
Net operating revenues	(9.0)	$ (2.4)
Assets	$ 91.9		$ 98.9