RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Reclassified restructuring reserves between segments			$ 9.8
Goodwill, Acquired During Period	$ 58.0	$ 398.3
Restructuring Reserve	67.3		82.3
Restructuring Charges	4.3
Restructuring Reserve Settled With Cash And Other Adjustment	18.9
Net restructuring charges	3.9	19.2
Restructuring charges related to severance and other employee costs	2.7	4.5
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	1.6	17.0
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	0.4	2.3
Reduction in total prior restructuring accruals	(0.4)
Restructuring Reserve, Current	34.6
Restructuring Reserve, Noncurrent	32.7
special charge - consulting expense	2.6
Special charge, wind-down of min volume contract		1.6
Special charge, accelerated equity compensation	0.9	1.2
Special charge, accelerated equity compensation	0.9	4.1
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	1.8	0.0
Net restructuring charges	2.4	16.0
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	19.6		28.2
Restructuring Charges	0.8
Restructuring Reserve Settled With Cash And Other Adjustment	9.3
Reduction in total prior restructuring accruals	0.1
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	30.8		32.5
Restructuring Charges	1.7
Restructuring Reserve Settled With Cash And Other Adjustment	(3.4)
Reduction in total prior restructuring accruals	0.0
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	56.2	398.3
Net restructuring charges	1.5	3.2
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	3.7		7.5
Restructuring Charges	1.8
Restructuring Reserve Settled With Cash And Other Adjustment	(5.3)
Reduction in total prior restructuring accruals	(0.3)
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	13.2		$ 14.1
Restructuring Charges	0.0
Restructuring Reserve Settled With Cash And Other Adjustment	0.9
Reduction in total prior restructuring accruals	0.0
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Other Special Charges	$ 2.7	1.5
Covance [Member]
Restructuring Cost and Reserve [Line Items]
Business Acquisition, Transaction Costs		$ 1.7