POSTRETIREMENT BENEFIT PLANS - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) category	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) category	Jun. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of categories | category	3		3
Defined contribution plan costs	$ 87	$ 90	$ 182	$ 191
Other pension plans
Defined Benefit Plan Disclosure [Line Items]
Threshold to be included in other pension plans	50		50
Principal retiree benefit plans
Defined Benefit Plan Disclosure [Line Items]
Plans cost (income)	$ (22)	$ (30)	(54)	$ (91)
Curtailment/settlement loss (gain)			$ (33)