Litigation, Claims and Contingencies - Summary of Reconciliation of Changes in Environmental Remediation Reserves (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Environmental Remediation Obligations [Abstract]
Environmental remediation reserve - beginning of year	$ 163	$ 177
Disbursements	(37)	(32)
Revised obligation estimates and accretion	61	18
Environmental remediation reserve - end of year	$ 187	$ 163

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Amount of expense (reversal of expense) which increases (decreases) the accrual for environmental loss contingencies from revisions in estimates to existing obligations. Excludes changes related to business acquisitions, divestitures, or currency movement.

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Amount of cash outflow to settle environmental loss contingencies.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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