PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 35	$ 48	$ 57
Interest cost	264	277	265
Expected return on plan assets	(409)	(495)	(476)
Amortization of actuarial loss	195	156	182
Amortization of prior service cost (credit)	4	4	4
Change in control enhanced benefits	0	5
Net periodic benefit cost (credit)	89	(5)	32
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	8	8	9
Expected return on plan assets	0	0	0
Amortization of actuarial loss	8	9	10
Amortization of prior service cost (credit)	(8)	(7)	(9)
Change in control enhanced benefits	0	0
Net periodic benefit cost (credit)	8	10	10
Plum Creek | Pension
Defined Benefit Plan Disclosure [Line Items]
Change in control enhanced benefits	0	5	0
Plum Creek | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Change in control enhanced benefits	0	$ 0	0
Discontinued operations | Cellulose Fibers | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13		$ 17