BUSINESS SEGMENT INFORMATION - Schedule of Segment Reporting Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Revenues	$ 701.3	$ 674.9	$ 2,062.9	$ 1,999.4
Direct costs	578.6	526.6	1,690.2	1,606.1
Selling, general and administrative expenses	106.8	136.3	353.4	412.6
Depreciation	19.6	21.2	58.7	64.5
Goodwill and other asset impairments	0.0	0.0	797.9	0.0
Operating loss	(8.6)	(18.0)	(859.0)	(106.3)
Interest expense	(22.6)	(22.4)	(68.2)	(101.9)
Foreign exchange loss	(2.6)	(0.2)	(28.1)	(7.0)
Other, net	5.1	4.8	7.9	15.1
Loss from continuing operations before income taxes	(28.7)	(35.8)	(947.4)	(200.1)
Corporate, non-segment
Segment Reporting Information [Line Items]
Corporate costs not included in segment operating income	10.0	33.8	49.5	107.3
Clinical Services Segment
Segment Reporting Information [Line Items]
Amortization	14.8	15.2	43.9	45.6
Goodwill and other asset impairments	0.0	0.0	797.9	0.0
Restructuring and other charges	4.9	8.8	21.7	22.5
Operating loss	(8.6)	(18.0)	(859.0)	(106.3)
Interest expense	(22.6)	(22.4)	(68.2)	(101.9)
Foreign exchange loss	(2.6)	(0.2)	(28.1)	(7.0)
Other, net	5.1	4.8	7.9	15.1
Loss from continuing operations before income taxes	(28.7)	(35.8)	(947.4)	(200.1)
Clinical Services Segment | Operating segments
Segment Reporting Information [Line Items]
Revenues	701.3	674.9	2,062.9	1,999.4
Pass through costs	280.0	228.0	796.2	677.9
Direct costs	298.5	299.0	891.3	927.2
Selling, general and administrative expenses	96.9	102.1	306.6	306.3
Depreciation	4.8	6.0	14.8	18.9
Segment operating income	$ 21.1	$ 39.8	$ 54.0	$ 69.1