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GOODWILL AND INTANGIBLE ASSETS (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, Written off Related to Sale of Business Unit			$ 12.6
Amortization of intangibles and other assets	$ 61.7	$ 54.7	179.0	$ 175.5
Severance Costs			26.2	$ 30.0
Intangible Assets, Gross (Excluding Goodwill)	5,798.2		5,798.2		$ 5,515.9
Balance as of January 1			7,360.3
Goodwill, Acquired During Period			540.0
Adjustments to goodwill			(72.4)
Balance at end of period	7,815.3		7,815.3
Finite-Lived Intangible Assets, Accumulated Amortization	1,776.9		1,776.9		1,604.8
Intangible Assets, Net (Excluding Goodwill)	4,021.3		4,021.3		3,911.1
LabCorp Diagnostics [Member]
Goodwill [Line Items]
Goodwill, Written off Related to Sale of Business Unit			0.0
Balance as of January 1			3,638.8
Goodwill, Acquired During Period			72.8
Adjustments to goodwill			0.9
Balance at end of period	3,712.5		3,712.5
Covance Drug Development [Member]
Goodwill [Line Items]
Goodwill, Written off Related to Sale of Business Unit			12.6
Balance as of January 1			3,721.5
Goodwill, Acquired During Period			467.2
Adjustments to goodwill			(73.3)
Balance at end of period	4,102.8		4,102.8
Customer Relationships [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,370.9		4,370.9		4,119.4
Finite-Lived Intangible Assets, Accumulated Amortization	1,274.5		1,274.5		1,146.7
Intangible Assets, Net (Excluding Goodwill)	3,096.4		3,096.4		2,972.7
Patents, Licenses And Technology [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	450.2		450.2		447.3
Finite-Lived Intangible Assets, Accumulated Amortization	229.0		229.0		211.2
Intangible Assets, Net (Excluding Goodwill)	221.2		221.2		236.1
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	89.4		89.4		76.8
Finite-Lived Intangible Assets, Accumulated Amortization	58.4		58.4		53.7
Intangible Assets, Net (Excluding Goodwill)	31.0		31.0		23.1
Trade Names [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	405.4		405.4		404.0
Finite-Lived Intangible Assets, Accumulated Amortization	209.8		209.8		189.1
Intangible Assets, Net (Excluding Goodwill)	195.6		195.6		214.9
Use Rights [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	11.1		11.1		10.8
Finite-Lived Intangible Assets, Accumulated Amortization	5.2		5.2		4.1
Intangible Assets, Net (Excluding Goodwill)	5.9		5.9		6.7
Canadian licenses [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	471.2		471.2		457.6
Finite-Lived Intangible Assets, Accumulated Amortization	0.0		0.0		0.0
Intangible Assets, Net (Excluding Goodwill)	$ 471.2		$ 471.2		$ 457.6