RESTRUCTURING RESERVES (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2020
Restructuring Cost and Reserve [Line Items]
Unused facility restructuring reserves	$ 7,800,000	$ 200,000
Balance, beginning of period	13,400,000
Restructuring charges	24,700,000
Cash payments and other adjustments	(50,800,000)
Balance, end of period	10,400,000	13,400,000
Current			$ 8,100,000
Non-current			2,300,000
Total Restructuring Reserve	10,400,000	13,400,000	10,400,000
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	1,100,000	400,000
LabCorp Diagnostics [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	500,000
Restructuring charges	3,900,000
Cash payments and other adjustments	(4,400,000)
Balance, end of period	0	500,000
Total Restructuring Reserve	0	500,000	0
LabCorp Diagnostics [Member] | Lease and Other Facility Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	2,700,000
Restructuring charges	5,200,000
Cash payments and other adjustments	(12,200,000)
Balance, end of period	1,500,000	2,700,000
Total Restructuring Reserve	1,500,000	2,700,000	1,500,000
Covance Drug Development [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	5,500,000
Restructuring charges	8,900,000
Cash payments and other adjustments	(10,400,000)
Balance, end of period	4,000,000.0	5,500,000
Total Restructuring Reserve	4,000,000.0	5,500,000	4,000,000.0
Covance Drug Development [Member] | Lease and Other Facility Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	4,700,000
Restructuring charges	6,700,000
Cash payments and other adjustments	(23,800,000)
Balance, end of period	4,900,000	4,700,000
Total Restructuring Reserve	$ 4,900,000	$ 4,700,000	$ 4,900,000