GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 275,400,000	$ 243,200,000	$ 231,700,000
Adjustments to intangibles through amortization expense	0.0	400,000	4,500,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Asset	10,800,000	3,300,000
Finite-Lived Intangible Assets, Future Amortization Expense
Estimated amortization expense, 2013	365,500,000
Estimated amortization expense, 2014	220,800,000
Estimated amortization expense, 2015	217,800,000
Estimated amortization expense, 2016	213,200,000
Estimated amortization expense, 2017	200,800,000
Estimated amortization expense, Thereafter	2,160,500,000
Goodwill, Impairment Loss	422,400,000	0
Goodwill and Intangible Asset Impairment	462,100,000	0	$ 0
Covance Drug Development [Member]
Finite-Lived Intangible Assets, Future Amortization Expense
Goodwill, Impairment Loss	418,700,000	0
Impairment of Intangible Assets (Excluding Goodwill)	31,800,000
Goodwill and Intangible Asset Impairment	450,500,000
Covance Drug Development [Member] | Trademarks and Trade Names [Member]
Finite-Lived Intangible Assets, Future Amortization Expense
Amortization	27,500,000
LabCorp Diagnostics [Member]
Finite-Lived Intangible Assets, Future Amortization Expense
Goodwill, Impairment Loss	3,700,000	$ 0
Impairment of Intangible Assets (Excluding Goodwill)	7,900,000
Goodwill and Intangible Asset Impairment	$ 11,600,000