RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 13.2		$ 13.4
Restructuring Charges	8.8
Restructuring Reserve Settled With Cash And Other Adjustment	(25.6)
Net restructuring charges	25.4	$ 20.6
Restructuring charges related to severance and other employee costs	5.1	16.8
Other Asset Impairment Charges	4.7
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	15.8	3.3
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment		(0.5)
Asset Impairment Charges	4.7
Operating Lease, Impairment Loss	11.6
Unused facility restructuring reserves	(0.2)
Reduction in total prior restructuring accruals	0.3
Restructuring Reserve, Current	7.8
Restructuring Reserve, Noncurrent	5.4
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Net restructuring charges	17.3	7.5
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	4.2		5.5
Restructuring Charges	2.5
Restructuring Reserve Settled With Cash And Other Adjustment	(4.4)
Asset Impairment Charges	0.0
Operating Lease, Impairment Loss	0.0
Reduction in total prior restructuring accruals	(0.6)
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	6.7		4.7
Restructuring Charges	2.7
Restructuring Reserve Settled With Cash And Other Adjustment	(12.2)
Asset Impairment Charges	4.7
Operating Lease, Impairment Loss	6.8
Reduction in total prior restructuring accruals	0.0
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Net restructuring charges	8.1	$ 13.1
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2.2		0.5
Restructuring Charges	2.1
Restructuring Reserve Settled With Cash And Other Adjustment	(0.3)
Asset Impairment Charges	0.0
Operating Lease, Impairment Loss	0.0
Reduction in total prior restructuring accruals	(0.1)
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0.1		$ 2.7
Restructuring Charges	1.5
Restructuring Reserve Settled With Cash And Other Adjustment	(8.7)
Asset Impairment Charges	0.0
Operating Lease, Impairment Loss	4.8
Reduction in total prior restructuring accruals	$ (0.2)