INCOME TAXES - Items Included in Our Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Postretirement benefits	$ 37	$ 50
Pension	75	306
State tax credits	51	56
Other reserves	13	38
Depletion	41	40
Excess interest	30	0
Incentive compensation	20	23
Workers compensation	18	19
Net operating loss carryforwards	19	18
Other	83	70
Gross deferred tax assets	387	620
Valuation allowance	(61)	(63)
Net deferred tax assets	326	557
Property, plant and equipment	(197)	(154)
Timber installment notes	(116)	(116)
Other	(41)	(19)
Net deferred tax liabilities	(354)	(289)
Net deferred tax asset (liability)	$ (28)	$ 268