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		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	$ 2.6
Provision for Doubtful Accounts	2.6	$ 2.8	$ 4.6	$ 2.8
Securities [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	0.2		0.3
Commercial Hedging [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	1.1		2.7
Allowance for Doubtful Accounts Receivable, Write-offs	0.3
Allowance for Doubtful Accounts Receivable, Recoveries	0.1
Physical Commodities [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	$ 1.3		$ 1.5