Segment Analysis (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 6,074.4	$ 3,399.9
Operating revenues	185.5	151.3
Net operating revenues	114.3	102.7
Net Segment Contribution	93.4	85.5
Segment Income	50.2	51.4
Costs not allocated to operating segments	41.8	39.3
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	8.4	12.1
Assets	6,290.7		$ 5,950.3
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues	57.5	55.4
Operating revenues	57.5	55.4
Net operating revenues	45.6	44.3
Net Segment Contribution	33.4	31.7
Segment Income	15.4	15.0
Assets	1,658.9		1,637.5
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues	23.1	18.3
Operating revenues	23.1	18.3
Net operating revenues	20.6	16.3
Net Segment Contribution	16.4	13.0
Segment Income	13.2	10.0
Assets	119.8		191.4
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	37.4	48.8
Operating revenues	37.4	48.8
Net operating revenues	25.1	36.0
Net Segment Contribution	19.8	29.5
Segment Income	12.9	21.9
Assets	2,470.2		2,130.7
Physical Commodities [Member]
Segment Reporting Information [Line Items]
Revenues	5,898.7	3,254.5
Operating revenues	9.8	5.9
Net operating revenues	8.1	4.7
Net Segment Contribution	5.8	3.4
Segment Income	3.0	1.0
Assets	313.9		258.0
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	63.6	29.8
Operating revenues	63.6	29.8
Net operating revenues	24.1	10.4
Net Segment Contribution	18.0	7.9
Segment Income	5.7	3.5
Assets	1,620.3		1,617.4
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	(5.9)	(6.9)
Operating revenues	(5.9)	(6.9)
Net operating revenues	(9.2)	$ (9.0)
Assets	$ 107.6		$ 115.3