GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 7,362.7		$ 7,362.7		$ 7,400.9	$ 6,424.4
Amortization of intangible assets	54.7	$ 54.6	175.5	$ 153.6
Finite-Lived Intangible Assets, Future Amortization Expense
Estimated amortization expense, 2012	51.3		51.3
Estimated amortization expense, 2013	222.5		222.5
Estimated amortization expense, 2014	214.4		214.4
Estimated amortization expense, 2015	208.1		208.1
Estimated amortization expense, 2016	202.5		202.5
Estimated amortization expense, Thereafter	2,522.8		2,522.8
LabCorp Diagnostics [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	3,649.5		3,649.5		3,673.9	3,644.8
Covance Drug Development [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 3,713.2		$ 3,713.2		$ 3,727.0	$ 2,779.6