Restructuring - Summary of Restructuring Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost And Reserve [Line Items]
Beginning balance	$ 2	$ 13
Restructuring costs		2
Cash payments	(2)	(13)
Ending balance		2
Employee-Related Costs
Restructuring Cost And Reserve [Line Items]
Beginning balance	2	12
Cash payments	$ (2)	(10)
Ending balance		2
Real Estate Costs
Restructuring Cost And Reserve [Line Items]
Beginning balance		1
Restructuring costs		2
Cash payments		$ (3)
Ending balance