Segment Analysis (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Sep. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 8,452.9	$ 11,769.3	$ 16,361.6	$ 23,906.8
Gross Profit	129.2	114.9	242.1	233.3
Net operating revenues	85.9	75.1	159.3	158.4
Net Contribution	65.9	55.6	123.1	114.0
Net Segment Income	36.5	26.0	65.9	55.3
Costs not allocated	26.2	24.3	51.7	39.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	10.3	1.7	14.2	15.7
Assets	3,015.1		3,015.1		2,848.0
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues	63.8	51.7	109.4	101.2
Gross Profit	63.8	51.7	109.4	101.2
Net operating revenues	52.6	41.5	88.8	82.4
Net Contribution	38.3	29.5	65.1	61.0
Net Segment Income	22.6	13.4	34.7	29.4
Assets	1,330.4		1,330.4		1,005.1
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues	12.8	9.3	26.4	19.4
Gross Profit	12.8	9.3	26.4	19.4
Net operating revenues	11.0	8.0	22.8	17.3
Net Contribution	8.6	6.2	17.8	13.1
Net Segment Income	6.3	4.6	13.3	9.6
Assets	44.0		44.0		57.2
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	17.2	18.0	38.6	32.7
Gross Profit	17.2	18.0	38.6	32.7
Net operating revenues	11.8	13.3	27.4	24.0
Net Contribution	8.9	10.6	20.8	18.9
Net Segment Income	3.8	5.4	11.0	9.6
Assets	207.2		207.2		204.2
Physical Commodities [Member]
Segment Reporting Information [Line Items]
Revenues	8,328.8	11,660.0	16,129.8	23,687.3
Gross Profit	5.1	5.6	10.3	13.8
Net operating revenues	4.2	4.6	8.7	11.7
Net Contribution	3.6	3.0	7.2	8.8
Net Segment Income	1.7	0.9	3.5	5.0
Assets	167.5		167.5		132.5
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	30.9	30.8	58.4	58.0
Gross Profit	30.9	30.8	58.4	58.0
Net operating revenues	8.4	8.2	15.5	15.5
Net Contribution	6.5	6.3	12.2	12.2
Net Segment Income	2.1	1.7	3.4	1.7
Assets	1,150.7		1,150.7		1,333.3
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	(0.6)	(0.5)	(1.0)	8.2
Gross Profit	(0.6)	(0.5)	(1.0)	8.2
Net operating revenues	(2.1)	(0.5)	(3.9)	7.5
Assets	$ 115.3		$ 115.3		$ 115.7