SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - NET SALES (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification									$ 1.6	$ 10.2	$ 16.9
Percent of Revenue Contributed									100.00%	100.00%	100.00%
Intercompany revenue elimination									$ 23.4	$ 10.5	$ 1.8
Revenues	$ 2,953.4	$ 2,928.5	$ 2,881.7	$ 2,791.2	$ 2,787.5	$ 2,831.3	$ 2,866.3	$ 2,848.3	11,554.8	11,333.4	10,308.0
Cash and Cash Equivalents, Period Increase (Decrease)									$ (89.3)	$ 110.2	$ (116.9)
LabCorp Diagnostics [Member]
Percent of Revenue Contributed									60.00%	62.00%	67.00%
Revenues									$ 7,000.1	$ 7,030.8	$ 6,858.2
Covance Drug Development [Member]
Percent of Revenue Contributed									40.00%	38.00%
Revenues									$ 4,578.1	$ 4,313.1	$ 3,451.6