RESTRUCTURING - Schedule of Restructuring Reserve Activity (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Mar. 31, 2024	Dec. 31, 2023
Restructuring Reserve [Roll Forward]
Beginning of period	$ 712		$ 0		$ 0
Restructuring charges	291
Change in estimate	(66)
Net restructuring charges	225	$ 781	0	$ 1,000	781
Payments and utilization	(173)				(69)
Foreign exchange	0				0
End of period	764	712		764	712
Personnel costs
Restructuring Reserve [Roll Forward]
Beginning of period	687		0		0
Restructuring charges	237
Change in estimate	(66)
Net restructuring charges	171				687
Payments and utilization	(127)				0
Foreign exchange	0				0
End of period	731	687		731	687
Other
Restructuring Reserve [Roll Forward]
Beginning of period	25		$ 0		0
Restructuring charges	54
Change in estimate	0
Net restructuring charges	54				94
Payments and utilization	(46)				(69)
Foreign exchange	0				0
End of period	$ 33	$ 25		$ 33	$ 25