Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Sep. 30, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives		$ 188	$ 159
Accumulated Amortization		(24)	(22)
Net Intangible Assets, finite lives		164	137
Developed Technologies [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	[1]	72	49
Accumulated Amortization	[1]	(7)	(7)
Net Intangible Assets, finite lives	[1]	65	42
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	[1]	18	16
Accumulated Amortization	[1]	(2)	(1)
Net Intangible Assets, finite lives	[1]	16	15
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	[1]	98	94
Accumulated Amortization	[1]	(15)	(14)
Net Intangible Assets, finite lives	[1]	$ 83	$ 80

[1] The changes in the gross carrying value of the Developed technologies, Trademarks, and Customer relationships intangible assets are primarily due to the acquisition of Tech Blend as described in Note C.