INCOME TAXES - Items Included in Our Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Postretirement benefits	$ 50	$ 76
Pension	306	395
State tax credits	56	46
Other reserves	38	14
Net operating loss carryforwards	18	25
Other	152	218
Gross deferred tax assets	620	774
Valuation allowance	(63)	(56)
Net deferred tax assets	557	718
Property, plant and equipment	(154)	(214)
Timber installment notes	(116)	(180)
Other	(19)	(31)
Deferred tax liabilities	(289)	(425)
Net deferred tax asset (liability)	$ 268	$ 293