SEGMENT INFORMATION - Segment Financial Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total net sales	$ 2,368.4	$ 2,001.7	$ 2,236.3	$ 1,593.6	$ 1,117.8	$ 1,077.8	$ 1,111.7	$ 1,056.2	$ 8,200.0	$ 4,363.5	$ 3,881.7
Income (loss) from operations	226.1	$ 169.1	$ 200.6	$ 67.3	93.4	$ 125.2	$ 123.5	$ 131.3	663.1	473.4	421.1
Interest expense and other, net									(216.3)	(105.8)	(69.0)
Income (loss) from operations before income taxes									446.8	367.6	352.1
Depreciation and amortization									401.4	109.3	103.2
Capital expenditures									185.3	93.3	89.5
Segment assets	18,944.2				8,649.2				18,944.2	8,649.2	6,580.0
Freight Segment
Segment Reporting Information [Line Items]
Total net sales									5,441.4	1,766.4	1,538.6
Transit Segment
Segment Reporting Information [Line Items]
Total net sales									2,758.6	2,597.1	2,343.1
Operating Segments | Freight Segment
Segment Reporting Information [Line Items]
Total net sales									5,501.0	1,819.2	1,577.6
Income (loss) from operations									642.9	334.3	271.7
Interest expense and other, net									0.0	0.0	0.0
Income (loss) from operations before income taxes									642.9	334.3	271.7
Depreciation and amortization									330.4	41.6	43.1
Capital expenditures									105.1	24.6	32.2
Segment assets	14,450.9				3,329.6				14,450.9	3,329.6	3,104.9
Operating Segments | Transit Segment
Segment Reporting Information [Line Items]
Total net sales									2,782.0	2,608.4	2,348.6
Income (loss) from operations									214.4	192.5	177.2
Interest expense and other, net									0.0	0.0	0.0
Income (loss) from operations before income taxes									214.4	192.5	177.2
Depreciation and amortization									62.2	62.7	58.0
Capital expenditures									63.7	61.6	52.5
Segment assets	6,026.0				9,478.6				6,026.0	9,478.6	7,885.3
Corporate Activities and Elimination
Segment Reporting Information [Line Items]
Total net sales									(83.0)	(64.1)	(44.5)
Income (loss) from operations									(194.2)	(53.4)	(27.8)
Interest expense and other, net									(216.3)	(105.8)	(69.0)
Income (loss) from operations before income taxes									(410.5)	(159.2)	(96.8)
Depreciation and amortization									8.8	5.0	2.1
Capital expenditures									16.5	7.1	4.8
Segment assets	$ (1,532.7)				$ (4,159.0)				(1,532.7)	(4,159.0)	(4,410.2)
Corporate Activities and Elimination | Freight Segment
Segment Reporting Information [Line Items]
Total net sales									59.6	52.8	39.0
Corporate Activities and Elimination | Transit Segment
Segment Reporting Information [Line Items]
Total net sales									$ 23.4	$ 11.3	$ 5.5