GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 7,423.3		$ 7,423.3		$ 7,400.9	$ 6,424.4
Amortization of intangible assets	58.5	$ 51.4	120.8	$ 99.0
Finite-Lived Intangible Assets, Future Amortization Expense
Estimated amortization expense, 2012	109.6		109.6
Estimated amortization expense, 2013	225.0		225.0
Estimated amortization expense, 2014	216.9		216.9
Estimated amortization expense, 2015	210.6		210.6
Estimated amortization expense, 2016	204.5		204.5
Estimated amortization expense, Thereafter	2,526.9		2,526.9
LabCorp Diagnostics [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	3,674.4		3,674.4		3,673.9	3,644.8
Covance Drug Development [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 3,748.9		$ 3,748.9		$ 3,727.0	$ 2,779.6