Segment Analysis Level 4 (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Sep. 30, 2011
Segment Reporting Information [Line Items]
Revenues	$ 17,351.1	$ 20,573.4	$ 51,592.5	$ 51,427.2
Gross Profit	123.8	105.4	339.7	315.1
Net Contribution	61.3	59.8	169.0	169.7
Net Segment Income	30.2	34.8	80.1	99.4
Costs not allocated	24.3	17.5	71.3	52.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	5.9	17.3	8.8	46.5
Assets	2,734.4		2,734.4		2,635.7
Commodity and Risk Management [Member]
Segment Reporting Information [Line Items]
Revenues	17,266.8	20,518.5	51,341.5	51,274.3
Gross Profit	67.0	65.5	182.7	189.1
Net Contribution	38.3	41.0	105.1	112.7
Net Segment Income	18.9	25.4	50.0	69.8
Assets	1,444.0		1,444.0		1,540.8
Foreign Exchange Segment [Member]
Segment Reporting Information [Line Items]
Revenues	16.5	14.3	47.4	41.8
Gross Profit	16.5	14.3	47.4	41.8
Net Contribution	11.3	9.1	31.6	26.2
Net Segment Income	7.7	6.6	21.9	19.3
Assets	133.9		133.9		146.1
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	8.6	5.5	28.8	23.2
Gross Profit	8.6	5.5	28.8	23.2
Net Contribution	4.8	3.1	14.4	12.3
Net Segment Income	1.1	(0.2)	3.0	1.0
Assets	63.3		63.3		104.8
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	27.7	15.9	70.8	51.3
Gross Profit	27.7	15.9	70.8	51.3
Net Contribution	4.2	4.3	10.5	12.3
Net Segment Income	1.0	1.7	1.6	6.0
Assets	989.4		989.4		734.4
Other Segment [Member]
Segment Reporting Information [Line Items]
Revenues	31.3	18.3	104.5	36.1
Gross Profit	3.8	3.3	10.5	9.2
Net Contribution	2.7	2.3	7.4	6.2
Net Segment Income	1.5	1.3	3.6	3.3
Assets	24.1		24.1		43.4
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	0.2	0.9	(0.5)	0.5
Gross Profit	0.2	0.9	(0.5)	0.5
Assets	$ 79.7		$ 79.7		$ 66.2