Significant Accounting Policies - Schedule of Change Retrospectively to Prior Periods Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017	Oct. 01, 2016
Significant Accounting Policies [Line Items]
Inventories	$ 478	$ 433
Deferred income taxes (assets)	27	237
Retained earnings	$ 1,555	1,707
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]
Inventories		433
Deferred income taxes (assets)		237
Retained earnings		1,707	$ 1,561
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]
Inventories		396
Deferred income taxes (assets)		250
Retained earnings		1,683	1,544
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]
Inventories		37
Deferred income taxes (assets)		(13)
Retained earnings		$ 24	$ 17