Commitments and Contingent Liabilities Commitments and Contingencies Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014
Loss Contingencies [Line Items]
Environmental remediation costs	$ 61.4	$ 60.0
Conditional asset retirement obligations	20.2	22.2
Indemnification liabilities	114.2	117.9
Recorded probable expected recoveries	(33.2)	(40.0)
Net recorded liabilities	81.0	77.9
Indemnification Agreement [Member]
Loss Contingencies [Line Items]
Other current liabilities	3.2	2.9
Other liabilities	29.4	32.8
Indemnification liabilities	32.6	35.7
Receivables	(2.1)	(2.1)
Other assets	(22.6)	(24.6)
Recorded probable expected recoveries	(24.7)	(26.7)
Net recorded liabilities	7.9	9.0
Substantially Indemnified by ExxonMobil Corporation [Member] | Indemnification Agreement [Member]
Loss Contingencies [Line Items]
Indemnification liabilities	26.0	27.9
Recorded probable expected recoveries	$ (24.7)	$ (26.7)