Acquisitions and Divestitures - Schedule of Aggregate Cash Consideration and Total Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Inventories	$ 3	$ 1	$ 0
Other current assets	1	0	0
Property, plant and equipment	99	6	19
Operating lease assets	38	1	0
Goodwill	207	17	50
Other current liabilities	(9)	(1)	0
Operating lease liabilities	(35)	0	0
Other noncurrent liabilities	(84)	(4)	(1)
Net assets acquired	282	40	82
Bargain purchase gain	0	0	(4)
Consideration transferred	$ 282	40	78
Weighted average useful life	10 years
Assets Held under Capital and Finance Leases
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired Assumed, Finance Lease Asset	$ 84
Capital Lease Obligations
Business Acquisition [Line Items]
Business combination Recognized Identifiable Liabilities Assumed, Finance Lease Obligation, Current	4
Business Combination, Recognized Identifiable Asset Acquired and Liability Assumed, Lease Obligation	80
Reacquired franchise rights
Business Acquisition [Line Items]
Intangible assets	$ 59	$ 20	$ 5
Weighted average useful life	10 years	10 years	9 years
Gain (Loss) on Contract Termination	$ 0
Customer relationships
Business Acquisition [Line Items]
Intangible assets	0	$ 0	$ 6
Trademarks and trade names
Business Acquisition [Line Items]
Intangible assets	0	0	1
Other intangible assets
Business Acquisition [Line Items]
Intangible assets	$ 3	$ 0	$ 2