Significant Accounting Policies - Schedule of Change Retrospectively to Prior Periods Consolidated Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Significant Accounting Policies [Line Items]
Net income (loss)	$ 99	$ 55	$ (176)	$ 194
Deferred tax provision (benefit)			131	(25)
Inventories			$ (77)	(61)
Change in Method of Accounting for Inventories from Last-in, First-out Method to First-in, First-out Method [Member]
Significant Accounting Policies [Line Items]
Net income (loss)		55		194
Deferred tax provision (benefit)				(25)
Inventories				(61)
Change in Method of Accounting for Inventories from Last-in, First-out Method to First-in, First-out Method [Member] | As Originally Reported [Member]
Significant Accounting Policies [Line Items]
Net income (loss)		53		191
Deferred tax provision (benefit)				(26)
Inventories				(57)
Change in Method of Accounting for Inventories from Last-in, First-out Method to First-in, First-out Method [Member] | Effect of Change [Member]
Significant Accounting Policies [Line Items]
Net income (loss)		$ 2		3
Deferred tax provision (benefit)				1
Inventories				$ (4)