Inventories - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Inventory Disclosure [Abstract]
Inventory valued under the LIFO method	7.00%	8.00%
Inventory, LIFO reserve	$ 37	$ 27
Increase (Decrease) in cost of sales	0	0	$ 1
Effect of LIFO inventory liquidation on income	$ 0	$ 0	$ (1)
Liquidation of LIFO inventory, resulted per diluted common share	$ 0.00	$ 0.00	$ 0.01
Obsolete inventory reserve	$ 19	$ 20
Lower of cost or market reserve inventory	$ 4		$ 6