Acquisitions and Divestitures - Schedule of Aggregate Cash Consideration and Total Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Inventories	$ 2	$ 1	$ 1
Other current assets	1	0	1
Property, plant and equipment	2	2	9
Goodwill	58	60	94
Other noncurrent assets	0	0	3
Trade and other payables	0	0	(11)
Debt	0	0	(11)
Other noncurrent liabilities	0	0	(9)
Net assets acquired	125	72	79
Goodwill not expected to be deductible for tax purposes			83
Trademarks and trade names
Business Acquisition [Line Items]
Intangible assets	$ 27	1	1
Weighted average useful life	19 years
Reacquired franchise rights
Business Acquisition [Line Items]
Intangible assets	$ 26	6	0
Purchase accounting adjustment, increase in finite lived intangible assets		6
Weighted average useful life	8 years
Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 9	2	0
Weighted average useful life	13 years
Other intangible assets
Business Acquisition [Line Items]
Intangible assets	$ 0	$ 0	$ 1