Debt - Schedule of Receivables Facility (Details) - Energy Services - Receivables Facility - Energy Services Receivables Facility - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Short-term Debt
Trade receivables transferred to ESFC during the year	$ 1,017.3	$ 756.4	$ 1,037.8
ESFC trade receivables sold to the bank during the year	243.0	204.0	306.5
ESFC trade receivables - end of year	44.8	35.7	$ 44.1
Outstanding balance of trade receivables sold	$ 39.0	$ 25.5