Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 5	$ 5	$ 4
Charged to expenses	2	1	1
Charged to other accounts	1	0	0
Deductions	(1)	(1)	0
Balance at end of period	7	5	5
Inventory excess and obsolete reserves
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	3	2	2
Charged to expenses	0	1	0
Charged to other accounts	0	0	0
Deductions	0	0	0
Balance at end of period	3	3	2
Deferred tax asset valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	8	12	7
Charged to expenses	0	0	0
Charged to other accounts	0	0	5
Deductions	(1)	(4)	0
Balance at end of period	$ 7	$ 8	$ 12