RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	$ 54.9		$ 1,009.8
Restructuring Reserve	53.1		54.7
Restructuring Charges	27.9
Restructuring Reserve Settled With Cash And Other Adjustment	(28.1)
Net restructuring charges	26.5	$ 43.0
Restructuring charges related to severance and other employee costs	23.1	22.5
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs	2.5	5.9
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment	0.5	0.4
Asset Impairment Charges	2.3	15.1
Unused facility restructuring reserves	0.9	0.1
Reduction in total prior restructuring accruals	(1.4)
Restructuring Reserve, Current	25.5
Restructuring Reserve, Noncurrent	27.6
special charge - consulting expense	4.5	4.9
Business Combination, Acquisition Related Costs		6.6
Special charge, accelerated equity compensation		0.9
Special charge, accelerated equity compensation	37.6
Special charge - one-time tax liability	31.0
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	51.0		811.3
Net restructuring charges	17.4	34.1
Asset Impairment Charges	2.3
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	11.9		8.3
Restructuring Charges	15.7
Restructuring Reserve Settled With Cash And Other Adjustment	(11.2)
Reduction in total prior restructuring accruals	0.9
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	31.5		34.6
Restructuring Charges	2.6
Restructuring Reserve Settled With Cash And Other Adjustment	(5.7)
Reduction in total prior restructuring accruals	0.0
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period	3.9		198.5
Net restructuring charges	9.1	8.9
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2.0		1.7
Restructuring Charges	7.4
Restructuring Reserve Settled With Cash And Other Adjustment	(7.1)
Reduction in total prior restructuring accruals	0.0
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	7.7		$ 10.1
Restructuring Charges	2.2
Restructuring Reserve Settled With Cash And Other Adjustment	(4.1)
Reduction in total prior restructuring accruals	(0.5)
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Other Special Charges	$ 4.2	$ 5.5