RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	$ 540.0
Restructuring Reserve	14.8		$ 43.6
ASC 842 Lease Adoption Implementation Impact	(32.8)
Restructuring Charges	34.6
Restructuring Reserve Settled With Cash And Other Adjustment	44.4
Net restructuring charges	48.4	$ 36.5
Restructuring charges related to severance and other employee costs	26.2	30.0
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	22.0	8.8
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	(0.4)	(1.1)
Asset Impairment Charges	0.0	5.3
Unused facility restructuring reserves	(0.2)	1.2
Reduction in total prior restructuring accruals	0.2
Operating Lease, Impairment Loss	13.6
Restructuring Reserve, Current	11.1
Restructuring Reserve, Noncurrent	3.7
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	467.2
Net restructuring charges	25.6	23.3
Asset Impairment Charges	5.3
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	10.9
Restructuring Reserve Settled With Cash And Other Adjustment	11.0
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	4.7		27.6
ASC 842 Lease Adoption Implementation Impact	(27.1)
Restructuring Charges	1.8
Restructuring Reserve Settled With Cash And Other Adjustment	(10.0)
Reduction in total prior restructuring accruals	0.1
Operating Lease, Impairment Loss	12.5
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	72.8
Net restructuring charges	22.8	$ 13.2
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	15.3
Restructuring Reserve Settled With Cash And Other Adjustment	17.0
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	6.6
Restructuring Reserve Settled With Cash And Other Adjustment	6.4
Reduction in total prior restructuring accruals	(0.1)
Operating Lease, Impairment Loss	$ 1.1