ACCUMULATED OTHER COMPREHENSIVE LOSS - Changes in Amounts Included in Our Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	$ 8,731
Translation adjustments	9	$ (42)
Total other comprehensive income	30	3
Balance at end of period	9,328	8,082
Pension
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(1,064)	(1,128)
Other comprehensive income (loss) before reclassifications	(4)	20
Amounts reclassified from accumulated other comprehensive loss to earnings	24	24
Total other comprehensive income	20	44
Balance at end of period	(1,044)	(1,084)
Other Post-Employment Benefits
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(12)	(12)
Amounts reclassified from accumulated other comprehensive loss to earnings	1	1
Total other comprehensive income	1	1
Balance at end of period	(11)	(11)
Translation Adjustment and Other
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	254	236
Translation adjustments	9	(42)
Total other comprehensive income	9	(42)
Balance at end of period	263	194
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(822)	(904)
Total other comprehensive income	30	3
Balance at end of period	$ (792)	$ (901)