RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Mar. 31, 2016
Restructuring Cost and Reserve [Line Items]
Reclassified restructuring reserves between segments				$ 9.8
Goodwill, Acquired During Period		$ 141.3		398.3
Restructuring Reserve		69.9		82.3
Restructuring Charges		43.5
Restructuring Reserve Settled With Cash And Other Adjustment		55.4
Net restructuring charges		43.0	$ 25.8
Restructuring charges related to severance and other employee costs		22.5	9.0
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs		5.9	21.6
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment		0.4	2.6
Asset Impairment Charges		15.1	0.0
Unused facility restructuring reserves		0.1	2.2
Reduction in total prior restructuring accruals		(0.5)
Restructuring Reserve, Current		37.8
Restructuring Reserve, Noncurrent		32.1
special charge - consulting expense		4.9
Special charge, wind-down of min volume contract	$ 2.7
Special charge, accelerated equity compensation	1.7	0.9
Special charge, accelerated equity compensation	4.5	6.6
Special charge - one-time tax liability	1.1		1.1
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period		1.8		0.0
Net restructuring charges		34.1	23.0
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		21.3		28.2
Restructuring Charges		15.8
Restructuring Reserve Settled With Cash And Other Adjustment		22.6
Reduction in total prior restructuring accruals		0.1
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		31.3		32.5
Restructuring Charges		18.4
Restructuring Reserve Settled With Cash And Other Adjustment		(19.6)
Reduction in total prior restructuring accruals		0.0
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period		139.5		398.3
Net restructuring charges		8.9	$ 2.8
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		3.4		7.5
Restructuring Charges		6.7
Restructuring Reserve Settled With Cash And Other Adjustment		(10.5)
Reduction in total prior restructuring accruals		(0.3)
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		13.9		$ 14.1
Restructuring Charges		2.6
Restructuring Reserve Settled With Cash And Other Adjustment		2.7
Reduction in total prior restructuring accruals		(0.1)
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Other Special Charges	$ 3.4	$ 5.5
Covance [Member]
Restructuring Cost and Reserve [Line Items]
Business Acquisition, Transaction Costs					$ 5.7