RESTRUCTURING RESERVES (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Unused facility restructuring reserves	$ 1.2	$ 0.1
special charge - consulting expense	4.3	8.0
Special charge, accelerated equity compensation		0.9
Balance, beginning of period	54.7
Restructuring charges	38.8
Reduction of prior restructuring accruals	(2.3)
Cash payments and other adjustments	(43.1)
Balance, end of period	48.1
Current			$ 22.6
Non-current			25.5
Total Restructuring Reserve	54.7		48.1
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	1.1	$ 1.4
LabCorp Diagnostics [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	1.7
Restructuring charges	10.7
Reduction of prior restructuring accruals	0.0
Cash payments and other adjustments	(11.1)
Balance, end of period	1.3
Total Restructuring Reserve	1.7		1.3
LabCorp Diagnostics [Member] | Lease and Other Facility Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	10.1
Restructuring charges	3.0
Reduction of prior restructuring accruals	(0.5)
Cash payments and other adjustments	(5.3)
Balance, end of period	7.3
Total Restructuring Reserve	10.1		7.3
Covance Drug Development [Member] | Severance and Other Employee Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	8.3
Restructuring charges	19.3
Reduction of prior restructuring accruals	1.2
Cash payments and other adjustments	(16.3)
Balance, end of period	10.1
Total Restructuring Reserve	8.3		10.1
Covance Drug Development [Member] | Lease and Other Facility Costs [Member]
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	34.6
Restructuring charges	5.8
Reduction of prior restructuring accruals	0.6
Cash payments and other adjustments	(10.4)
Balance, end of period	29.4
Total Restructuring Reserve	$ 34.6		$ 29.4