Receivables from customers, net and notes receivable, net - Allowance for Bad Debts Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Receivables from customers and notes receivable, net [Abstract]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	$ 48.6	$ 58.2	$ 54.6	$ 9.7
Allowance for Doubtful Accounts Receivable [Roll Forward]
Provision for bad debts	(9.8)	3.9	51.0
Allowance for Doubtful Accounts Receivable, Charge-offs	1.3	0.3	6.1
Allowance for Doubtful Accounts Receivable, Recoveries	0.4	0.1
SEC Schedule, 12-09, Valuation Allowances and Reserves, Increase (Decrease) Adjustment	$ 1.5	$ 0.0	$ 0.0