Receivables from customers, net and notes receivable, net - Allowance for Bad Debts Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 11.2	$ 5.8	$ 1.2
Provision for bad debts		4.2	6.0	$ 5.3
Allowance for Doubtful Accounts Receivable, Charge-offs	(0.4)	(5.7)	(0.6)	(0.7)
Allowance for Doubtful Accounts Receivable, Recoveries	0.2
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 9.7	$ 11.2	$ 5.8	$ 1.2