GOODWILL AND INTANGIBLE ASSETS (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Goodwill [Line Items]
Severance Costs	$ 23.1	$ 22.5
Intangible Assets, Gross (Excluding Goodwill)	5,562.3		$ 5,566.2
Balance as of January 1	7,400.9
Goodwill, Acquired During Period	54.9		1,009.8
Goodwill, Written off Related to Sale of Business Unit	0.0		(170.5)
Adjustments to goodwill	(32.5)		137.2
Balance at end of period	7,423.3		7,400.9
Finite-Lived Intangible Assets, Accumulated Amortization	1,512.8		1,400.1
Intangible Assets, Net (Excluding Goodwill)	4,049.5		4,166.1
LabCorp Diagnostics [Member]
Goodwill [Line Items]
Balance as of January 1	3,673.9
Goodwill, Acquired During Period	3.9		198.5
Goodwill, Written off Related to Sale of Business Unit	0.0		(170.5)
Adjustments to goodwill	(3.4)		1.1
Balance at end of period	3,674.4		3,673.9
Covance Drug Development [Member]
Goodwill [Line Items]
Balance as of January 1	3,727.0
Goodwill, Acquired During Period	51.0		811.3
Goodwill, Written off Related to Sale of Business Unit	0.0		0.0
Adjustments to goodwill	(29.1)		136.1
Balance at end of period	3,748.9		3,727.0
Customer Relationships [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,138.5		4,118.1
Finite-Lived Intangible Assets, Accumulated Amortization	1,075.5		992.8
Intangible Assets, Net (Excluding Goodwill)	3,063.0		3,125.3
Patents, Licenses And Technology [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	452.2		457.9
Finite-Lived Intangible Assets, Accumulated Amortization	202.1		188.6
Intangible Assets, Net (Excluding Goodwill)	250.1		269.3
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	75.7		75.8
Finite-Lived Intangible Assets, Accumulated Amortization	51.5		48.3
Intangible Assets, Net (Excluding Goodwill)	24.2		27.5
Trade Names [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	410.0		407.9
Finite-Lived Intangible Assets, Accumulated Amortization	180.3		167.9
Intangible Assets, Net (Excluding Goodwill)	229.7		240.0
Use Rights [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	10.8		10.8
Finite-Lived Intangible Assets, Accumulated Amortization	3.4		2.5
Intangible Assets, Net (Excluding Goodwill)	7.4		8.3
Canadian licenses [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	475.1		495.7
Finite-Lived Intangible Assets, Accumulated Amortization	0.0		0.0
Intangible Assets, Net (Excluding Goodwill)	$ 475.1		$ 495.7

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