BASIS OF FINANCIAL STATEMENT PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Asset Impairment Charges	$ 0.0		$ 0.0		$ 437.4	$ 0.0
Revenues	2,768.8		2,881.7		5,592.6	5,672.9
Cost of Revenue	2,008.3		2,056.9		4,104.1	4,058.4
Contract with Customer, Liability	471.4				471.4		$ 449.2
Amortization of Deferred Sales Commissions	5.5		$ 5.1		10.8	9.5
Assets, Current	$ 3,413.2				3,413.2		2,981.2
Net Cash Provided by (Used in) Operating Activities					$ 574.5	$ 419.3
Percent of Revenue Contributed	100.00%		100.00%		100.00%	100.00%
Selling, general and administrative expenses	$ 396.3		$ 415.3		$ 791.8	$ 809.1
Nonoperating Income (Expense)	(0.7)		(65.7)		(75.8)	(129.2)
Provision for income taxes	65.4		79.3		114.6	148.1
Net earnings	231.6		190.7		(85.3)	376.6
Net Income (Loss) Attributable to Parent	$ 231.6	$ (317.2)	$ 190.4	$ 185.6	$ (85.6)	$ 376.0
Basic earnings per common share (in dollars per share)	$ 2.38		$ 1.94		$ (0.88)	$ 3.82
Diluted earnings per common share (in dollars per share)	$ 2.37		$ 1.93		$ (0.88)	$ 3.79
Net Cash Provided by (Used in) Investing Activities					$ (230.0)	$ (891.3)
Net Cash Provided by (Used in) Financing Activities					(119.7)	311.7
Effect of exchange rate changes on cash and cash equivalents					(5.3)	(1.1)
Assets	$ 17,849.1				17,849.1		18,046.4
Long-term debt, less current portion	3,034.4				3,034.4		2,655.8
Common stock, 92.8 and 93.5 shares outstanding at March 31, 2013 and December 31, 2012, respectively	19.5				19.5		20.1
Stockholders' Equity Attributable to Parent	7,352.7	7,020.1	$ 7,144.4	7,111.3	7,352.7	7,144.4	7,567.0	$ 6,971.4
Liabilities and Equity	17,849.1				17,849.1		18,046.4
Capitalized Contract Cost, Amortization	2.3		1.9		5.3	3.8
Deferred Revenue, Revenue Recognized					102.2	161.6
Revenue, Remaining Performance Obligation, Amount	4,498.8				4,498.8
Contract with Customer, Performance Obligation Satisfied in Previous Period					13.7	48.4
Goodwill, Impairment Loss					422.4
Other than Temporary Impairment Losses, Investments					25.4
Cash Payment Received Appropriated by U.S. Congress Covid-19					$ 55.9
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	$ 1,692.7		$ 1,760.9		$ 3,394.7	$ 3,482.9
Percent of Revenue Contributed	61.00%		61.00%		60.00%	61.00%
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	$ 1,093.7		$ 1,126.3		$ 2,237.5	$ 2,201.0
Percent of Revenue Contributed	39.00%				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	$ 5.2	13.1			18.3
Retained Earnings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Income (Loss) Attributable to Parent	231.6	(317.2)	190.4	185.6
Stockholders' Equity Attributable to Parent	$ 7,760.6	$ 7,529.0	$ 7,455.8	$ 7,265.4	$ 7,760.6	$ 7,455.8	$ 7,903.6	$ 7,079.8