SEGMENT AND CUSTOMER REPORTING - Schedule of Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Total segment income	$ 128.8	$ 125.8
Finance costs	13.7	14.0
Miscellaneous expense	1.4	6.6
Employee SBC expense	26.0	22.7
Total return swap (TRS) fair value adjustments	19.1	(31.5)
Amortization of intangible assets (excluding computer software)	11.1	10.2
Restructuring and other charges, net of recoveries	3.9	4.8
Earnings before income taxes	113.7	105.2
Operating Segments
Segment Reporting Information [Line Items]
Total segment income	187.8	130.6
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment
Segment Reporting Information [Line Items]
Finance costs	13.7	14.0
Miscellaneous expense	1.4	6.6
Foreign currency forward contracts transitional adjustments	0.0	(0.5)
Employee SBC expense	26.0	22.7
Total return swap (TRS) fair value adjustments	19.1	(31.5)
Amortization of intangible assets (excluding computer software)	10.0	9.3
Restructuring and other charges, net of recoveries	3.9	4.8
ATS | Operating Segments
Segment Reporting Information [Line Items]
Total segment income	$ 40.7	$ 31.9
Segment margin, percentage	5.00%	4.20%
CCS | Operating Segments
Segment Reporting Information [Line Items]
Total segment income	$ 147.1	$ 98.7
Segment margin, percentage	8.00%	6.80%