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GOODWILL AND INTANGIBLE ASSETS (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ 60.2	$ 58.5	117.3	$ 120.8
Severance Costs			20.3	$ 23.1
Intangible Assets, Gross (Excluding Goodwill)	5,738.0		5,738.0		$ 5,515.9
Balance as of January 1			7,360.3
Goodwill, Acquired During Period			490.5
Adjustments to goodwill			5.5
Balance at end of period	7,843.7		7,843.7
Finite-Lived Intangible Assets, Accumulated Amortization	1,722.1		1,722.1		1,604.8
Intangible Assets, Net (Excluding Goodwill)	4,015.9		4,015.9		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			22.3
Adjustments to goodwill			1.9
Balance at end of period	3,663.0		3,663.0
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			468.2
Adjustments to goodwill			3.6
Balance at end of period	4,180.7		4,180.7
Customer Relationships [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,307.9		4,307.9		4,119.4
Finite-Lived Intangible Assets, Accumulated Amortization	1,233.0		1,233.0		1,146.7
Intangible Assets, Net (Excluding Goodwill)	3,074.9		3,074.9		2,972.7
Patents, Licenses And Technology [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	452.3		452.3		447.3
Finite-Lived Intangible Assets, Accumulated Amortization	224.1		224.1		211.2
Intangible Assets, Net (Excluding Goodwill)	228.2		228.2		236.1
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	82.5		82.5		76.8
Finite-Lived Intangible Assets, Accumulated Amortization	57.2		57.2		53.7
Intangible Assets, Net (Excluding Goodwill)	25.3		25.3		23.1
Trade Names [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	407.7		407.7		404.0
Finite-Lived Intangible Assets, Accumulated Amortization	202.9		202.9		189.1
Intangible Assets, Net (Excluding Goodwill)	204.8		204.8		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	4.9		4.9		4.1
Intangible Assets, Net (Excluding Goodwill)	6.2		6.2		6.7
Canadian licenses [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	476.5		476.5		457.6
Finite-Lived Intangible Assets, Accumulated Amortization	0.0		0.0		0.0
Intangible Assets, Net (Excluding Goodwill)	$ 476.5		$ 476.5		$ 457.6