Acquisitions and Divestitures - Schedule of Aggregate Cash Consideration and Total Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions			12 Months Ended
	Jul. 13, 2018	Oct. 02, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory			$ 1	$ 0	$ 2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other			0	0	1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment			6	19	2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Asset			1	0	0
Goodwill			17	50	58
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other			(4)	(1)	0
Net assets acquired			40	82	125
Bargain purchase gain			0	(4)	0
Consideration transferred	$ 53	$ 60	$ 40	78	125
Weighted average useful life			10 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Liabilities			$ (1)	0	0
Reacquired franchise rights
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			$ 20	5	26
Weighted average useful life			10 years
Customer relationships
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			$ 0	6	9
Trademarks and trade names
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			0	1	27
Other intangible assets
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			$ 0	$ 2	$ 0