GOODWILL AND INTANGIBLE ASSETS (Changes in Carrying Amount of Goodwill) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Amortization of intangibles and other assets	$ 60,100,000	$ 60,200,000	$ 122,400,000	$ 117,300,000
Severance Costs			10,500,000	$ 20,300,000
Intangible Assets, Gross (Excluding Goodwill)	5,848,100,000		5,848,100,000			$ 5,885,600,000
Balance as of January 1			7,865,000,000.0
Adjustments to goodwill			(28,000,000.0)
Balance at end of period	7,422,700,000		7,422,700,000
Finite-Lived Intangible Assets, Accumulated Amortization	1,970,900,000		1,970,900,000			1,851,100,000
Intangible Assets, Net (Excluding Goodwill)	3,877,200,000		3,877,200,000			4,034,500,000
Goodwill, Impairment Loss			422,400,000
Goodwill, Acquired During Period			8,100,000
LabCorp Diagnostics [Member]
Goodwill [Line Items]
Goodwill and Intangible Asset Impairment			11,000,000.0
Balance as of January 1			3,721,500,000
Adjustments to goodwill			6,400,000
Balance at end of period	3,732,300,000		3,732,300,000
Goodwill, Impairment Loss			3,700,000
Percentage Fair Value of Goodwill Exceeded Carrying Value					10.00%
Percentage Change in Discount Rate Used to Calculate Fair Value of Goodwill					1.00%
Value of Goodwill Impairment Following a Percentage Change in the Discount Rate Used to Calculate Goodwill for Reporting Unit					$ 40,000,000.0
Value of Reporting Units Goodwill Fair Value Exceeds Carrying Value	84.4		84.4
Goodwill, Acquired During Period			8,100,000
Covance Drug Development [Member]
Goodwill [Line Items]
Goodwill and Intangible Asset Impairment			426,400,000
Balance as of January 1			4,143,500,000
Adjustments to goodwill			(34,400,000)
Balance at end of period	3,690,400,000		3,690,400,000
Goodwill, Impairment Loss			418,700,000
Percentage Fair Value of Goodwill Exceeded Carrying Value					10.00%
Percent Change in Discount Rate Used to Calculate Fair Value of Goodwill for Reporting Unit					1.00%
Percent of Fair Value Exceeding Carrying Value Post Percent Change in Discount Rate Used to Calculate Fair Value of Goodwill for Reporting Unit					2.00%
Value of Reporting Unit's Goodwill Following Impairment					$ 1,560,500,000
Value of Reporting Units Goodwill Fair Value Exceeds Carrying Value	628,500,000		628,500,000
Goodwill, Acquired During Period			0
Customer Relationships [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,424,300,000		4,424,300,000			4,441,700,000
Finite-Lived Intangible Assets, Accumulated Amortization	1,419,900,000		1,419,900,000			1,329,500,000
Intangible Assets, Net (Excluding Goodwill)	3,004,400,000		3,004,400,000			3,112,200,000
Patents, Licenses And Technology [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	449,000,000.0		449,000,000.0			453,600,000
Finite-Lived Intangible Assets, Accumulated Amortization	245,500,000		245,500,000			235,700,000
Intangible Assets, Net (Excluding Goodwill)	203,500,000		203,500,000			217,900,000
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	96,200,000		96,200,000			90,900,000
Finite-Lived Intangible Assets, Accumulated Amortization	65,000,000.0		65,000,000.0			60,500,000
Intangible Assets, Net (Excluding Goodwill)	31,200,000		31,200,000			30,400,000
Trade Names [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	408,100,000		408,100,000			408,200,000
Finite-Lived Intangible Assets, Accumulated Amortization	234,300,000		234,300,000			219,900,000
Intangible Assets, Net (Excluding Goodwill)	173,800,000		173,800,000			188,300,000
Use Rights [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	10,800,000		10,800,000			10,900,000
Finite-Lived Intangible Assets, Accumulated Amortization	6,200,000		6,200,000			5,500,000
Intangible Assets, Net (Excluding Goodwill)	4,600,000		4,600,000			5,400,000
Canadian licenses [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	459,700,000		459,700,000			480,300,000
Finite-Lived Intangible Assets, Accumulated Amortization	0		0			0
Intangible Assets, Net (Excluding Goodwill)	$ 459,700,000		459,700,000			$ 480,300,000
Trade Names [Member] | Covance Drug Development [Member]
Goodwill [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)			$ 2,700,000