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, 2019	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Geographic Allocation of Income and Provision (Credit) for Income Taxes [Abstract]
Income (Loss) Before Income Taxes, Domestic		$ 696		$ 1,305	$ 856
Income (Loss) Before Income Taxes, Foreign		(5)		(3)	(6)
Income before income taxes		691		1,302	850
Current Federal Tax Expense (Benefit)		70		166	226
Current State and Local Tax Expense (Benefit)		4		6	2
Current Foreign Tax Expense (Benefit)		0		40	3
Current Income Tax Expense (Benefit)		74		212	231
Deferred Federal Income Tax Expense (Benefit)		(9)		27	392
Deferred State and Local Income Tax Expense (Benefit)		(1)		8	22
Deferred Income Tax Expense (Benefit)		(10)		35	414
Provision for income taxes		64		247	645
Net Income Attributable to Union Carbide Corporation		627		$ 1,055	205
Tax Cuts and Jobs Act, Change in Tax Rate, Income Tax Expense (Benefit)	$ 2		$ (248)		$ (250)
Tax Cuts and Jobs Act of 2017, Indirect Impact on Inventory, Provisional Income Tax Expense		$ (2)