Segment Analysis (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 3,995.1	$ 7,005.1	$ 32,064.8	$ 23,366.7
Operating revenues	151.6	118.2	445.6	360.3
Net operating revenues	103.4	76.0	304.5	235.3
Net Segment Contribution	77.9	58.7	231.5	181.8
Segment Income	45.4	29.5	135.4	95.4
Costs not allocated to operating segments	28.2	25.5	86.5	77.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	17.2	4.0	48.9	18.2
Assets	4,486.8		4,486.8		$ 3,039.7
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues	62.2	54.9	195.3	164.3
Operating revenues	62.2	54.9	195.3	164.3
Net operating revenues	50.3	44.1	161.0	132.9
Net Segment Contribution	34.5	32.2	114.4	97.3
Segment Income	18.7	16.6	65.3	51.3
Assets	1,184.6		1,184.6		1,400.9
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues	18.2	13.6	51.8	40.0
Operating revenues	18.2	13.6	51.8	40.0
Net operating revenues	16.3	11.9	45.9	34.7
Net Segment Contribution	13.0	9.3	36.6	27.1
Segment Income	10.2	7.0	28.3	20.3
Assets	55.5		55.5		51.9
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	36.5	20.0	89.8	58.6
Operating revenues	36.5	20.0	89.8	58.6
Net operating revenues	25.3	12.8	60.8	40.2
Net Segment Contribution	20.2	9.7	46.4	30.5
Segment Income	12.8	4.9	26.7	15.9
Assets	1,736.6		1,736.6		235.5
Physical Commodities [Member]
Segment Reporting Information [Line Items]
Revenues	3,847.6	6,890.5	31,636.2	23,020.3
Operating revenues	4.1	3.6	17.0	13.9
Net operating revenues	3.8	3.0	15.3	11.7
Net Segment Contribution	3.2	2.0	12.1	9.2
Segment Income	0.9	0.1	5.8	3.6
Assets	129.6		129.6		116.8
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	29.5	27.1	92.2	85.5
Operating revenues	29.5	27.1	92.2	85.5
Net operating revenues	9.0	6.5	27.7	22.0
Net Segment Contribution	7.0	5.5	22.0	17.7
Segment Income	2.8	0.9	9.3	4.3
Assets	1,282.0		1,282.0		1,136.2
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	1.1	(1.0)	(0.5)	(2.0)
Operating revenues	1.1	(1.0)	(0.5)	(2.0)
Net operating revenues	(1.3)	$ (2.3)	(6.2)	$ (6.2)
Assets	$ 98.5		$ 98.5		$ 98.4