Reportable Segment Information - Sales and Property, Plant and Equipment by Geographical Area (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Sales	$ 594	$ 577	$ 569	$ 545	$ 547	$ 534	$ 514	$ 489	$ 2,285	$ 2,084	$ 1,929
Property, plant and equipment - net	420				391				420	391
UNITED STATES
Segment Reporting Information [Line Items]
Sales									1,652	1,504	1,397
Property, plant and equipment - net	384				352				384	352
International
Segment Reporting Information [Line Items]
Sales									633	580	$ 532
Property, plant and equipment - net	$ 36				$ 39				$ 36	$ 39