RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	$ 22.1
Restructuring Reserve	15.7		$ 43.6
ASC 842 Lease Adoption Implementation Impact	(32.8)
Restructuring Charges	18.4
Restructuring Reserve Settled With Cash And Other Adjustment	15.7
Net restructuring charges	20.6	$ 14.3
Restructuring charges related to severance and other employee costs	16.8	11.3
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	3.3	1.2
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	0.5
Asset Impairment Charges	0.0	2.3
Unused facility restructuring reserves		0.5
Reduction in total prior restructuring accruals	0.5
Operating Lease, Impairment Loss	1.7
Restructuring Reserve, Current	15.7
Restructuring Reserve, Noncurrent	0.0
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	14.3
Net restructuring charges	7.5	10.7
Asset Impairment Charges	2.3
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	9.6		6.5
ASC 842 Lease Adoption Implementation Impact	0.0
Restructuring Charges	6.9
Restructuring Reserve Settled With Cash And Other Adjustment	4.2
Reduction in total prior restructuring accruals	(0.4)
Operating Lease, Impairment Loss	0.0
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2.1		27.6
ASC 842 Lease Adoption Implementation Impact	(27.1)
Restructuring Charges	0.2
Restructuring Reserve Settled With Cash And Other Adjustment	1.4
Reduction in total prior restructuring accruals	0.0
Operating Lease, Impairment Loss	0.0
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	7.8
Net restructuring charges	13.1	$ 3.6
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1.2		2.1
ASC 842 Lease Adoption Implementation Impact	0.0
Restructuring Charges	9.9
Restructuring Reserve Settled With Cash And Other Adjustment	10.9
Reduction in total prior restructuring accruals	0.1
Operating Lease, Impairment Loss	0.0
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2.8		$ 7.4
ASC 842 Lease Adoption Implementation Impact	(5.7)
Restructuring Charges	1.4
Restructuring Reserve Settled With Cash And Other Adjustment	2.0
Reduction in total prior restructuring accruals	0.0
Operating Lease, Impairment Loss	$ 1.7