POSTRETIREMENT BENEFIT PLANS - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) category	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) category	Sep. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of categories | category	3		3
Defined contribution plan costs	$ 71	$ 83	$ 253	$ 274
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)	$ (31)	$ (31)	(85)	$ (122)
Curtailment/settlement loss (gain)			$ (33)