INCOME TAXES (Schedule of Domestic and Foreign Components of Income Before Income Taxes and Tax Reconciliation) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense(Benefit)	$ 2	$ (248)		$ (250)
Tax Cuts and Jobs Act of 2017, Indirect Impact on Inventory, Provisional Income Tax Expense			$ (2)
Geographic Allocation of Income and Provision (Credit) for Income Taxes [Abstract]
Income (Loss) Before Income Taxes, Domestic			1,305	856	$ 49
Income (Loss) Before Income Taxes, Foreign			(3)	(6)	8
Income before income taxes			1,302	850	57
Current Federal Tax Expense (Benefit)			166	226	265
Current State and Local Tax Expense (Benefit)			6	2	(3)
Current Foreign Tax Expense (Benefit)			40	3	3
Current Income Tax Expense (Benefit)			212	231	265
Deferred Federal Income Tax Expense (Benefit)			27	392	(285)
Deferred State and Local Income Tax Expense (Benefit)			8	22	(12)
Deferred Income Tax Expense (Benefit)			35	414	(297)
Provision (Credit) for income taxes			247	645	(32)
Net Income Attributable to Union Carbide Corporation			$ 1,055	$ 205	$ 89