BASIS OF FINANCIAL STATEMENT PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 2,791.2	$ 2,848.3
Cost of Revenue	2,001.5	2,069.3
Contract with Customer, Liability	362.0		$ 354.1
Amortization of Deferred Sales Commissions	4.5	4.2
Assets, Current	2,885.3		2,835.4
Net Cash Provided by (Used in) Operating Activities	$ 165.8	$ 179.7
Percent of Revenue Contributed	100.00%	100.00%
Selling, general and administrative expenses	$ 393.8	$ 397.0
Nonoperating Income (Expense)	(63.5)	(63.9)
Provision for income taxes	68.8	69.0
Net earnings	185.9	172.5
Net Income (Loss) Attributable to Parent	$ 185.6	$ 173.2
Basic earnings per common share (in dollars per share)	$ 1.88	$ 1.70
Diluted earnings per common share (in dollars per share)	$ 1.86	$ 1.67
Net Cash Provided by (Used in) Investing Activities	$ (140.5)	$ (74.3)
Net Cash Provided by (Used in) Financing Activities	(103.2)	(65.0)
Effect of exchange rate changes on cash and cash equivalents	(0.1)	4.7
Cash and Cash Equivalents, Period Increase (Decrease)	(78.0)	45.1
Assets	16,970.8		16,185.3
Long-term debt, less current portion	2,526.9		1,878.9
Common stock, 92.8 and 93.5 shares outstanding at March 31, 2013 and December 31, 2012, respectively	19.5		19.1
Stockholders' Equity Attributable to Parent	7,111.3	6,984.0	6,971.4	$ 6,804.1
Liabilities and Equity	16,970.8		$ 16,185.3
Capitalized Contract Cost, Amortization	1.8	0.6
Deferred Revenue, Revenue Recognized	103.6
Revenue, Remaining Performance Obligation, Amount	3,950.4
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 39.7	22.1
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	$ 1,722.0	$ 1,770.2
Percent of Revenue Contributed	62.00%	62.00%
Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 1,074.7	$ 1,078.5
Percent of Revenue Contributed	38.00%