Receivables From Customers, Net and Notes Receivable, Net Receivables from Customers, Net and Notes Receivables, Net - Bad Debt Expense and Recoveries (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)			$ 2.8
Provision for Doubtful Accounts	$ 0.4	$ 4.6	3.2
Securities [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		0.3
Commercial Hedging [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		2.7
Allowance for Doubtful Accounts Receivable, Write-offs			$ 0.4
Physical Commodities [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		$ 1.5