Receivables from customers, net and notes receivable, net - Allowance for Bad Debts Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	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	$ 54.6	$ 9.7	$ 11.2	$ 5.8
Provision for bad debts			51.0	4.2	$ 6.0
Allowance for Doubtful Accounts Receivable, Charge-offs	$ (0.1)		(6.1)	(5.7)	(0.6)
Allowance for Doubtful Accounts Receivable, Recoveries		0.2
Allowance for Doubtful Accounts - Customer and Notes Receivable		$ 54.6	$ 9.7	$ 11.2	$ 5.8