BASIS OF FINANCIAL STATEMENT PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset Impairment Charges	$ 437.4	$ 0.0
Revenues	2,823.8	2,791.2
Cost of Revenue	2,095.8	2,001.5
Contract with Customer, Liability	430.9		$ 449.2
Amortization of Deferred Sales Commissions	5.3	4.5
Assets, Current	2,891.1		2,981.2
Net Cash Provided by (Used in) Operating Activities	$ 203.8	$ 165.8
Percent of Revenue Contributed	100.00%	100.00%
Selling, general and administrative expenses	$ 395.5	$ 393.8
Nonoperating Income (Expense)	(75.1)	(63.5)
Provision for income taxes	49.2	68.8
Net earnings	(316.9)	185.9
Net Income (Loss) Attributable to Parent	$ (317.2)	$ 185.6
Basic earnings per common share (in dollars per share)	$ (3.27)	$ 1.88
Diluted earnings per common share (in dollars per share)	$ (3.27)	$ 1.86
Net Cash Provided by (Used in) Investing Activities	$ (106.6)	$ (140.5)
Net Cash Provided by (Used in) Financing Activities	(102.8)	(103.2)
Effect of exchange rate changes on cash and cash equivalents	(8.3)	(0.1)
Assets	17,298.4		18,046.4
Long-term debt, less current portion	2,458.0		2,655.8
Common stock, 92.8 and 93.5 shares outstanding at March 31, 2013 and December 31, 2012, respectively	18.5		20.1
Stockholders' Equity Attributable to Parent	7,020.1	7,111.3	7,567.0	$ 6,971.4
Liabilities and Equity	17,298.4		18,046.4
Capitalized Contract Cost, Amortization	3.0	1.8
Deferred Revenue, Revenue Recognized	121.8	103.6
Revenue, Remaining Performance Obligation, Amount	4,494.9
Contract with Customer, Performance Obligation Satisfied in Previous Period	9.7	39.7
Goodwill, Impairment Loss	422.4
Other than Temporary Impairment Losses, Investments	$ 20.2
Ownership percentage below which investments are generally accounted for on the cost method (in thousandths)	20.00%
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(7.0)
LabCorp Diagnostics [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 1,702.0	$ 1,722.0
Percent of Revenue Contributed	60.00%	62.00%
Goodwill and Intangible Asset Impairment	$ 11.0
Goodwill, Impairment Loss	3.7
Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 1,143.8	$ 1,074.7
Percent of Revenue Contributed	40.00%
Goodwill and Intangible Asset Impairment	$ 426.4
Goodwill, Impairment Loss	418.7
Equity Method Income (Loss), Net [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other than Temporary Impairment Losses, Investments	7.1
Other Nonoperating Income (Expense) [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other than Temporary Impairment Losses, Investments	13.1
Retained Earnings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Income (Loss) Attributable to Parent	(317.2)	185.6
Stockholders' Equity Attributable to Parent	$ 7,529.0	$ 7,265.4	7,903.6	$ 7,079.8
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ (7.0)