GOODWILL AND INTANGIBLE ASSETS (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Goodwill [Line Items]
Severance Costs	$ 11.3	$ 2.7
Intangible Assets, Gross (Excluding Goodwill)	5,788.4		$ 5,767.7
Balance as of January 1	7,571.4
Goodwill, Acquired During Period	6.8	1,009.8
Adjustments to goodwill	37.3	137.2
Balance at end of period	7,615.5
Finite-Lived Intangible Assets, Accumulated Amortization	1,490.9		1,426.9
Intangible Assets, Net (Excluding Goodwill)	4,297.5		4,340.8
LabCorp Diagnostics [Member]
Goodwill [Line Items]
Balance as of January 1	3,844.4
Goodwill, Acquired During Period	3.9	198.5
Adjustments to goodwill	(1.8)	1.1
Balance at end of period	3,846.5
Covance Drug Development [Member]
Goodwill [Line Items]
Balance as of January 1	3,727.0
Goodwill, Acquired During Period	2.9	811.3
Adjustments to goodwill	39.1	$ 136.1
Balance at end of period	3,769.0
Customer Relationships [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,331.5		4,297.9
Finite-Lived Intangible Assets, Accumulated Amortization	1,062.4		1,014.9
Intangible Assets, Net (Excluding Goodwill)	3,269.1		3,283.0
Patents, Licenses And Technology [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	455.5		457.9
Finite-Lived Intangible Assets, Accumulated Amortization	195.9		188.6
Intangible Assets, Net (Excluding Goodwill)	259.6		269.3
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	78.9		79.0
Finite-Lived Intangible Assets, Accumulated Amortization	51.2		49.4
Intangible Assets, Net (Excluding Goodwill)	27.7		29.6
Trade Names [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	428.2		426.3
Finite-Lived Intangible Assets, Accumulated Amortization	178.3		171.4
Intangible Assets, Net (Excluding Goodwill)	249.9		254.9
Use Rights [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	10.9		10.9
Finite-Lived Intangible Assets, Accumulated Amortization	3.1		2.6
Intangible Assets, Net (Excluding Goodwill)	7.8		8.3
Canadian licenses [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	483.4		495.7
Finite-Lived Intangible Assets, Accumulated Amortization	0.0		0.0
Intangible Assets, Net (Excluding Goodwill)	$ 483.4		$ 495.7

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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