Segment and Geographic Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Revenues	$ 43,768.3	$ 67,959.3	$ 72,891.3
Operating revenues	478.4	454.2	419.1
Net Contribution	234.1	225.2	225.4
Net Segment Income	114.3	106.6	129.8
Costs not allocated	91.7	90.8	74.4
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	22.6	15.8	55.4
Assets	2,848.0	2,953.0	2,632.0
Commodity and Risk Management [Member]
Segment Reporting Information [Line Items]
Revenues	43,218.2	67,627.0	72,667.8
Operating revenues	221.7	242.5	248.5
Net Contribution	131.1	139.5	147.5
Net Segment Income	59.6	66.2	89.4
Assets	1,105.1	1,439.7	1,534.8
Foreign Exchange Segment [Member]
Segment Reporting Information [Line Items]
Revenues	66.9	62.6	59.3
Operating revenues	66.9	62.6	59.3
Net Contribution	44.0	41.3	37.1
Net Segment Income	29.8	28.3	28.0
Assets	145.0	124.5	146.1
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	61.1	39.9	30.5
Operating revenues	61.1	39.9	30.5
Net Contribution	30.5	19.8	16.5
Net Segment Income	13.9	4.5	1.9
Assets	198.5	88.7	104.8
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	100.8	93.8	66.1
Operating revenues	100.8	93.8	66.1
Net Contribution	15.3	14.3	14.3
Net Segment Income	1.9	2.2	4.9
Assets	1,246.4	1,090.9	734.4
Other Segment [Member]
Segment Reporting Information [Line Items]
Revenues	314.1	136.2	67.2
Operating revenues	20.7	15.6	14.3
Net Contribution	13.2	10.3	10.0
Net Segment Income	9.1	5.4	5.6
Assets	37.3	110.8	43.4
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	7.2	(0.2)	0.4
Operating revenues	7.2	(0.2)	0.4
Assets	$ 115.7	$ 98.4	$ 68.5