Accounting Changes Accounting Changes - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax (benefit) provision	$ (124)	$ 97	$ 44
Excess Tax Benefit from Share-based Compensation, Operating Activities	(77)	$ 0	$ 0
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax (benefit) provision	$ 77
Weighted Average Number of Shares Outstanding, Basic	1
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 77

Increase (Decrease) in number of weighted average basic shares outstanding during the period.

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- Definition

Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 20
-Section 55
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=96864182&loc=d3e11374-113907

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- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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