Significant Accounting Policies - Summary of Activity in Tax Valuation Allowances (Details) - Valuation Allowance of Deferred Tax Assets [Member] - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Reserves deducted from asset accounts [Roll Forward]
Beginning balance	$ 79	$ 122	$ 136
Adjustments to net income	8	(5)	27
Reserves utilized	(4)	(38)	(41)
Ending balance	$ 83	$ 79	$ 122

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of valuation and qualifying accounts and reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

+ Details

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- Definition

Amount of increase in valuation and qualifying accounts and reserves from charge to cost and expense.

+ References

+ Details

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- Definition

Amount of decrease in valuation and qualifying accounts and reserves.

+ References

+ Details

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- Details

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