Inventories - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Inventory Disclosure [Abstract]
Percentage of inventories utilizing LIFO cost flow assumption		7.00%
Obsolete inventory reserve	$ 38	$ 19
Lower of cost or market charge inventory	$ 13

Amount of valuation reserve for inventory.

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Name:	us-gaap_InventoryValuationReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant