PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Estimated Amortization from Cumulative Other Comprehensive Loss (Details) $ in Millions	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 115
Prior service cost (credit)	3
Net effect cost	118
Pension
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	108
Prior service cost (credit)	4
Net effect cost	112
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	7
Prior service cost (credit)	(1)
Net effect cost	$ 6