Consolidated Statements of Stockholders' Deficit - USD ($) shares in Millions	Total	Common stock	Paid-in capital	Retained deficit	Accumulated other comprehensive (loss) income	Ashland’s net investment
Common stock outstanding, beginning balance (in shares) at Sep. 30, 2015		0
Balance at beginning of period at Sep. 30, 2015	$ 617,000,000	$ 0	$ 0	$ 0	$ (61,000,000)	$ 678,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	273,000,000					273,000,000
Net transfers to Ashland	(1,500,000,000)					(1,500,000,000)
Contribution of net liabilities from Ashland	(439,000,000)				51,000,000	(490,000,000)
Issuance of common stock to Ashland and in connection with initial public offering, net of offering costs (in shares)		205
Issuance of common stock to Ashland and in connection with initial public offering, net of offering costs	712,000,000	$ 2,000,000	710,000,000
Dividends paid	$ 0
Repurchase of common stock (in shares)	0
Repurchase of common stock	$ 0
Currency translation adjustments	8,000,000				8,000,000
Amortization of pension and other postretirement prior service credits in income	(1,000,000)				(1,000,000)
Common stock outstanding, ending balance (in shares) at Sep. 30, 2016		205
Balance at end of period at Sep. 30, 2016	(330,000,000)	$ 2,000,000	710,000,000	0	(3,000,000)	(1,039,000,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	304,000,000			304,000,000
Contribution of net liabilities from Ashland	(10,000,000)			(55,000,000)	47,000,000	(2,000,000)
Net transfers from Ashland	5,000,000					5,000,000
Distribution of Ashland’s net investment			(710,000,000)	(326,000,000)		1,036,000,000
Dividends paid	(40,000,000)			(40,000,000)
Stock-based compensation	$ 5,000,000		5,000,000
Repurchase of common stock (in shares)	(2)	(2)
Repurchase of common stock	$ (50,000,000)			(50,000,000)
Currency translation adjustments	7,000,000				7,000,000
Amortization of pension and other postretirement prior service credits in income	$ (8,000,000)				(8,000,000)
Common stock outstanding, ending balance (in shares) at Sep. 30, 2017	203	203
Balance at end of period at Sep. 30, 2017	$ (117,000,000)	$ 2,000,000	5,000,000	(167,000,000)	43,000,000	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	166,000,000			166,000,000
Dividends paid	(58,000,000)			(58,000,000)
Stock-based compensation	$ 9,000,000		9,000,000
Repurchase of common stock (in shares)	(15)	(15)
Repurchase of common stock	$ (325,000,000)			(325,000,000)
Purchase of remaining ownership interest in subsidiary	(14,000,000)		(7,000,000)	(7,000,000)
Reclassification of income tax effects of U.S. tax reform				(8,000,000)	8,000,000
Currency translation adjustments	(10,000,000)				(10,000,000)
Amortization of pension and other postretirement prior service credits in income	$ (9,000,000)				(9,000,000)
Common stock outstanding, ending balance (in shares) at Sep. 30, 2018	188	188
Balance at end of period at Sep. 30, 2018	$ (358,000,000)	$ 2,000,000	$ 7,000,000	$ (399,000,000)	$ 32,000,000	$ 0