Commitments and Contingent Liabilities - Schedule of Indemnification Liabilities and Related Expected Recoveries (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Loss Contingencies [Line Items]
Environmental remediation costs	$ 61.6	$ 67.6
Conditional asset retirement obligations	21.9	21.2
Indemnification liabilities	93.0	100.8
Recorded probable expected recoveries	(14.1)	(17.8)
Net recorded liabilities	78.9	83.0
Indemnification Agreement
Loss Contingencies [Line Items]
Indemnification liabilities	9.5	12.0
Other current liabilities	1.6	2.5
Other liabilities	7.9	9.5
Receivables	(0.8)	(1.6)
Other assets	(3.6)	(4.6)
Recorded probable expected recoveries	(4.4)	(6.2)
Net recorded liabilities	$ 5.1	$ 5.8