Receivables from customers, net and notes receivable, net - Allowance for Bad Debts Rollforward (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 1.2	$ 1.0	$ 11.9
Provision for bad debts	5.3	0.2	0.4
Allowance for Doubtful Accounts Receivable, Charge-offs	(0.7)	0	(11.2)
Allowance for Doubtful Accounts Receivable, Recoveries	0	0	(0.1)
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 5.8	$ 1.2	$ 1.0