RESTRUCTURING - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended			36 Months Ended
	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2024	Mar. 31, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 28	$ 49	$ 46
Transit Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		25	40	32
Freight Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		3	9	$ 14
Integration 2.0
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 146
Payments for restructuring		48	39
Integration 2.0 | Maximum
Restructuring Cost and Reserve [Line Items]
Total expected costs						$ 170
Portfolio Optimization
Restructuring Cost and Reserve [Line Items]
Total expected costs	$ 70	70			$ 70
Restructuring charges		28	$ 28		$ 56
Portfolio Optimization | Transit Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		10
Portfolio Optimization | Freight Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 18