Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Income tax expense	$ 94	$ 38
Effective tax rate	111.90%	34.50%
Tax Cuts and Jobs Act of 2017, income tax expense (benefit)	$ 68
Increase in income tax resulting from U.S. tax reform legislation	67
Repatriation tax on unremitted non-U.S. earnings	4
Net deferred tax assets				$ 281
Gross liability	22
Foreign tax credits	18
Previously undistributed earnings to be repatriated	45
Liability for uncertain income tax positions	10
Tax Matters Agreement | Ashland
Income Tax Contingency [Line Items]
Due to (from) related party	81			74
Tax Matters Agreement | Ashland | Accrued expenses and other liabilities
Income Tax Contingency [Line Items]
Due to (from) related party	3			2
Ashland | Tax Matters Agreement | Ashland
Income Tax Contingency [Line Items]
Income tax expense	3
Tax Cuts and Jobs Act of 2017, income tax expense (benefit)	(3)
Increase in due to affiliates recognized in selling, general and administrative expense	7
Due to (from) related party	67			62
Ashland | Tax Matters Agreement | Ashland | Accrued expenses and other liabilities
Income Tax Contingency [Line Items]
Due to (from) related party	1			1
Ashland | Tax Matters Agreement | Ashland | Other noncurrent liabilities
Income Tax Contingency [Line Items]
Due to (from) related party	$ 66			$ 61
Scenario, Forecast
Income Tax Contingency [Line Items]
US corporate federal blended income tax rate			24.50%
Uncertain tax positions from decreases in positions taken in the next twelve months			$ 3