BASIS OF FINANCIAL STATEMENT PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 2,881.7		$ 2,866.3		$ 5,672.9	$ 5,714.6
Cost of Revenue	2,056.9		2,031.2		4,058.4	4,100.5
Contract with Customer, Liability	402.2				402.2		$ 354.1
Amortization of Deferred Sales Commissions	5.1		$ 4.4		9.5	8.6
Assets, Current	$ 2,848.6				2,848.6		2,835.4
Net Cash Provided by (Used in) Operating Activities					$ 419.3	$ 567.1
Percent of Revenue Contributed	100.00%		100.00%		100.00%	100.00%
Selling, general and administrative expenses	$ 415.3		$ 395.2		$ 809.1	$ 792.2
Nonoperating Income (Expense)	(65.7)		(56.5)		(129.2)	(120.4)
Provision for income taxes	79.3		78.6		148.1	147.6
Net earnings	190.7		234.1		376.6	406.6
Net Income (Loss) Attributable to Parent	$ 190.4	$ 185.6	$ 233.8	$ 173.2	$ 376.0	$ 407.0
Basic earnings per common share (in dollars per share)	$ 1.94		$ 2.29		$ 3.82	$ 3.99
Diluted earnings per common share (in dollars per share)	$ 1.93		$ 2.27		$ 3.79	$ 3.94
Net Cash Provided by (Used in) Investing Activities					$ (891.3)	$ (196.3)
Net Cash Provided by (Used in) Financing Activities					311.7	(458.1)
Effect of exchange rate changes on cash and cash equivalents					(1.1)	(7.9)
Cash and Cash Equivalents, Period Increase (Decrease)					(161.4)	(95.2)
Assets	$ 17,744.4				17,744.4		16,185.3
Long-term debt, less current portion	2,495.8				2,495.8		1,878.9
Common stock, 92.8 and 93.5 shares outstanding at March 31, 2013 and December 31, 2012, respectively	20.0				20.0		19.1
Stockholders' Equity Attributable to Parent	7,144.4	$ 7,111.3	$ 7,037.7	$ 6,984.0	7,144.4	7,037.7	6,971.4	$ 6,804.1
Liabilities and Equity	17,744.4				17,744.4		16,185.3
Capitalized Contract Cost, Amortization	1.9		1.9		3.8	2.5
Deferred Revenue, Revenue Recognized					161.6	135.6
Revenue, Remaining Performance Obligation, Amount	4,138.0				$ 4,138.0
Contract with Customer, Performance Obligation Satisfied in Previous Period	48.4		(12.5)
Prior Period Reclassification Adjustment						45.1	$ 44.4
Ownership percentage below which investments are generally accounted for on the cost method (in thousandths)					20.00%
LabCorp Diagnostics [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 1,760.9		$ 1,814.0		$ 3,482.9	$ 3,584.2
Percent of Revenue Contributed	61.00%		63.00%		61.00%	62.00%
Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 1,126.3		$ 1,054.2		$ 2,201.0	$ 2,132.6
Percent of Revenue Contributed	39.00%				39.00%