Significant Accounting Policies - Schedule of Change Retrospectively to Prior Periods Consolidated Statements of Operations (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Cost of sales	$ 655	$ 544
Gross profit	166	176
Selling and administrative expenses	73	70
Research and technical expenses	16	15
Income (loss) from operations	77	91
Other income (expense)	$ 6	11
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]
Cost of sales		544
Gross profit		176
Selling and administrative expenses		70
Research and technical expenses		15
Income (loss) from operations		91
Other income (expense)		11
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]
Cost of sales		542
Gross profit		178
Selling and administrative expenses		69
Research and technical expenses		15
Income (loss) from operations		94
Other income (expense)		8
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]
Cost of sales		2
Gross profit		(2)
Selling and administrative expenses		1
Income (loss) from operations		(3)
Other income (expense)		$ 3