Acquisitions and Divestitures - Schedule of Aggregate Cash Consideration and Total Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Inventories	$ 0	$ 2	$ 1
Other current assets	0	1	0
Property, plant and equipment	19	2	2
Goodwill	50	58	60
Other noncurrent liabilities	(1)	0	0
Net assets acquired	82	125	72
Bargain purchase gain	(4)	0	0
Consideration transferred	$ 78	125	72
Weighted average useful life	10 years
Reacquired franchise rights
Business Acquisition [Line Items]
Intangible assets	$ 5	26	6
Purchase accounting adjustment, increase in finite lived intangible assets		6
Weighted average useful life	9 years
Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 6	9	2
Trademarks and trade names
Business Acquisition [Line Items]
Intangible assets	1	27	1
Other intangible assets
Business Acquisition [Line Items]
Intangible assets	$ 2	$ 0	$ 0