RESTRUCTURING AND OTHER SPECIAL CHARGES (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 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		$ 817.2		398.3
Restructuring Reserve		63.3		82.3
Restructuring Charges		66.1
Restructuring Reserve Settled With Cash And Other Adjustment		83.6
Net restructuring charges		64.6	$ 48.6
Restructuring charges related to severance and other employee costs		27.2	23.1
Restructuring charges related to contractual obligations associated with leased facilities and other facility related costs		17.9	30.7
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment		1.5	2.4
Asset Impairment Charges		23.5	0.0
Unused facility restructuring reserves			2.8
Reduction in total prior restructuring accruals		(1.5)
Restructuring Reserve, Current		29.1
Restructuring Reserve, Noncurrent		34.2
special charge - consulting expense		8.0
Special charge, wind-down of min volume contract	$ 4.0
Business Combination, Acquisition Related Costs			7.4
Special charge, accelerated equity compensation	2.3	0.9
Special charge, accelerated equity compensation	7.4	29.8
Special charge - one-time tax liability	1.1		1.1
Amortization of Debt Discount (Premium)			5.6
Covance Drug Development [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period		676.6		0.0
Net restructuring charges		50.5	38.9
Asset Impairment Charges		20.9
Covance Drug Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		11.7		28.2
Restructuring Charges		18.5
Restructuring Reserve Settled With Cash And Other Adjustment		34.1
Reduction in total prior restructuring accruals		0.9
Covance Drug Development [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		36.3		32.5
Restructuring Charges		33.0
Restructuring Reserve Settled With Cash And Other Adjustment		(29.1)
Reduction in total prior restructuring accruals		0.1
LabCorp Diagnostics [Member]
Restructuring Cost and Reserve [Line Items]
Goodwill, Acquired During Period		140.6		398.3
Net restructuring charges		14.1	$ 9.7
LabCorp Diagnostics [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		2.1		7.5
Restructuring Charges		8.7
Restructuring Reserve Settled With Cash And Other Adjustment		(13.7)
Reduction in total prior restructuring accruals		(0.4)
LabCorp Diagnostics [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve		13.2		$ 14.1
Restructuring Charges		5.9
Restructuring Reserve Settled With Cash And Other Adjustment		6.7
Reduction in total prior restructuring accruals		(0.1)
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Other Special Charges	$ 8.1	$ 8.2
Covance [Member]
Restructuring Cost and Reserve [Line Items]
Business Acquisition, Transaction Costs					$ 5.5