RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	$ 490.5
Restructuring Reserve	12.6		$ 43.6
ASC 842 Lease Adoption Implementation Impact	(32.8)
Restructuring Charges	23.0
Restructuring Reserve Settled With Cash And Other Adjustment	32.4
Net restructuring charges	34.2	$ 26.5
Restructuring charges related to severance and other employee costs	20.3	23.1
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	13.5	2.5
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	0.4	0.5
Asset Impairment Charges	0.0	2.3
Unused facility restructuring reserves		0.9
Reduction in total prior restructuring accruals	0.4
Operating Lease, Impairment Loss	10.8
Restructuring Reserve, Current	10.4
Restructuring Reserve, Noncurrent	2.2
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	468.2
Net restructuring charges	18.1	17.4
Asset Impairment Charges	2.3
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	6.9		6.5
ASC 842 Lease Adoption Implementation Impact	0.0
Restructuring Charges	8.4
Restructuring Reserve Settled With Cash And Other Adjustment	8.5
Reduction in total prior restructuring accruals	(0.5)
Operating Lease, Impairment Loss	0.0
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2.5		27.6
ASC 842 Lease Adoption Implementation Impact	(27.1)
Restructuring Charges	1.7
Restructuring Reserve Settled With Cash And Other Adjustment	(7.2)
Reduction in total prior restructuring accruals	0.0
Operating Lease, Impairment Loss	7.5
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	22.3
Net restructuring charges	16.1	$ 9.1
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0.3		2.1
ASC 842 Lease Adoption Implementation Impact	0.0
Restructuring Charges	11.9
Restructuring Reserve Settled With Cash And Other Adjustment	13.6
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	2.9		$ 7.4
ASC 842 Lease Adoption Implementation Impact	(5.7)
Restructuring Charges	1.0
Restructuring Reserve Settled With Cash And Other Adjustment	3.1
Reduction in total prior restructuring accruals	0.0
Operating Lease, Impairment Loss	$ 3.3