ACCUMULATED OTHER COMPREHENSIVE LOSS - Changes in Amounts Included in Our Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period			$ 8,731
Translation adjustments	$ 15	$ 17	24	$ (25)
Total other comprehensive income	136	41	166	44
Balance at end of period	10,400	8,202	10,400	8,202
Pension
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(1,044)	(1,084)	(1,064)	(1,128)
Other comprehensive income before reclassifications	100	0	96	20
Amounts reclassified from accumulated other comprehensive loss to earnings	20	24	44	48
Total other comprehensive income	120	24	140	68
Balance at end of period	(924)	(1,060)	(924)	(1,060)
Other Post-Employment Benefits
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(11)	(11)	(12)	(12)
Amounts reclassified from accumulated other comprehensive loss to earnings	1	0	2	1
Total other comprehensive income	1	0	2	1
Balance at end of period	(10)	(11)	(10)	(11)
Translation Adjustment and Other
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	263	194	254	236
Translation adjustments	15	17	24	(25)
Total other comprehensive income	15	17	24	(25)
Balance at end of period	278	211	278	211
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(792)	(901)	(822)	(904)
Total other comprehensive income	136	41	166	44
Balance at end of period	$ (656)	$ (860)	$ (656)	$ (860)