PROPERTY, PLANT AND EQUIPMENT AND OPERATING LEASES - Operating Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Long-term (fixed)	$ 745	$ 834	$ 966
Long-term (variable)	118	136	177
Short-term	209	206	133
Total operating lease expense	$ 1,072	$ 1,176	$ 1,276