Goodwill and Other Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 84	$ 76
Accumulated amortization	(11)	(9)
Net carrying amount	73	67
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	30	29
Accumulated amortization	(3)	(2)
Net carrying amount	27	27
Reacquired franchise rights
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	36	32
Accumulated amortization	(5)	(4)
Net carrying amount	31	28
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	17	14
Accumulated amortization	(3)	(3)
Net carrying amount	14	11
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	1	1
Accumulated amortization	0	0
Net carrying amount	$ 1	$ 1