GOODWILL AND INTANGIBLE ASSETS (Changes in Carrying Amount of Goodwill) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Goodwill [Line Items]
Amortization of intangibles and other assets	$ 62,300,000	$ 57,100,000
Severance Costs	5,100,000	$ 16,800,000
Intangible Assets, Gross (Excluding Goodwill)	5,811,700,000		$ 5,885,600,000
Balance as of January 1	7,865,000,000.0
Adjustments to goodwill	(54,100,000)
Balance at end of period	7,388,500,000
Finite-Lived Intangible Assets, Accumulated Amortization	1,906,600,000		1,851,100,000
Intangible Assets, Net (Excluding Goodwill)	3,905,100,000		4,034,500,000
Goodwill, Impairment Loss	422,400,000
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	(6,600,000)
Balance at end of period	3,711,200,000
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	81.5
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	(47,500,000)
Balance at end of period	3,677,300,000
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	$ 1,554,700,000
Value of Reporting Units Goodwill Fair Value Exceeds Carrying Value	631,900,000
Customer Relationships [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,414,400,000		4,441,700,000
Finite-Lived Intangible Assets, Accumulated Amortization	1,371,000,000.0		1,329,500,000
Intangible Assets, Net (Excluding Goodwill)	3,043,400,000		3,112,200,000
Patents, Licenses And Technology [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	444,400,000		453,600,000
Finite-Lived Intangible Assets, Accumulated Amortization	238,700,000		235,700,000
Intangible Assets, Net (Excluding Goodwill)	205,700,000		217,900,000
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	90,700,000		90,900,000
Finite-Lived Intangible Assets, Accumulated Amortization	62,300,000		60,500,000
Intangible Assets, Net (Excluding Goodwill)	28,400,000		30,400,000
Trade Names [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	407,300,000		408,200,000
Finite-Lived Intangible Assets, Accumulated Amortization	228,800,000		219,900,000
Intangible Assets, Net (Excluding Goodwill)	178,500,000		188,300,000
Use Rights [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	10,800,000		10,900,000
Finite-Lived Intangible Assets, Accumulated Amortization	5,800,000		5,500,000
Intangible Assets, Net (Excluding Goodwill)	5,000,000.0		5,400,000
Canadian licenses [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	444,100,000		480,300,000
Finite-Lived Intangible Assets, Accumulated Amortization	0		0
Intangible Assets, Net (Excluding Goodwill)	444,100,000		$ 480,300,000
Trade Names [Member] | Covance Drug Development [Member]
Goodwill [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	$ 2,700,000