Goodwill and Other Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 175	$ 112
Accumulated amortization	(44)	(28)
Net carrying amount	131	84
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	30	30
Accumulated amortization	(8)	(6)
Net carrying amount	22	24
Reacquired franchise rights
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	116	57
Accumulated amortization	(25)	(14)
Net carrying amount	91	43
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	23	22
Accumulated amortization	(9)	(7)
Net carrying amount	14	15
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	6	3
Accumulated amortization	(2)	(1)
Net carrying amount	$ 4	$ 2