Receivables from customers, net and notes receivable, net - Bad Debt Expense and Recoveries (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Doubtful Accounts	$ 0.2	$ 0.5	$ 6.8
Allowance for Doubtful Accounts Receivable, Charge-offs	0	(11.2)	(113.3)
Allowance for Doubtful Accounts Receivable, Recoveries	0	(0.1)	(3.7)
Commodity and Risk Management [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Doubtful Accounts	0.7	0.7	4.5
Allowance for Doubtful Accounts Receivable, Charge-offs	0.6	0.3	1.4
Allowance for Doubtful Accounts Receivable, Recoveries	0.1	0.1	3.7
Consigned gold charge-off		8.5
CR&M customer deficit charge-off			3.7
CES Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
CES customer deficits charge-off		$ 2.7