RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 10,400,000	$ 13,400,000
Restructuring Charges	24,700,000
Restructuring Reserve Settled With Cash And Other Adjustment	(50,800,000)
Net restructuring charges	38,900,000	48,400,000
Restructuring charges related to severance and other employee costs	12,800,000	26,200,000
Other Asset Impairment Charges	11,000,000.0
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	24,000,000.0	22,000,000.0
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	(1,100,000)	(400,000)
Asset Impairment Charges	23,100,000
Unused facility restructuring reserves	(7,800,000)	(200,000)
Restructuring Reserve, Current	8,100,000
Restructuring Reserve, Noncurrent	2,300,000
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Net restructuring charges	25,500,000	25,600,000
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	4,000,000.0	5,500,000
Restructuring Charges	8,900,000
Restructuring Reserve Settled With Cash And Other Adjustment	(10,400,000)
Asset Impairment Charges	0
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	4,900,000	4,700,000
Restructuring Charges	6,700,000
Restructuring Reserve Settled With Cash And Other Adjustment	(23,800,000)
Asset Impairment Charges	17,300,000
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Net restructuring charges	13,400,000	22,800,000
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	500,000
Restructuring Charges	3,900,000
Restructuring Reserve Settled With Cash And Other Adjustment	(4,400,000)
Asset Impairment Charges	0
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1,500,000	$ 2,700,000
Restructuring Charges	5,200,000
Restructuring Reserve Settled With Cash And Other Adjustment	(12,200,000)
Asset Impairment Charges	$ 5,800,000