BASIS OF FINANCIAL STATEMENT PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 2,928.5			$ 2,831.3			$ 8,601.4	$ 8,545.9
Cost of Revenue	2,111.2			2,041.4			6,169.6	6,141.9
Contract with Customer, Liability	400.2						400.2		$ 354.1
Amortization of Deferred Sales Commissions	5.8			$ 4.2			15.3	12.8
Assets, Current	$ 2,987.8						2,987.8		2,835.4
Net Cash Provided by (Used in) Operating Activities							$ 874.9	$ 819.0
Percent of Revenue Contributed	100.00%			100.00%			100.00%	100.00%
Selling, general and administrative expenses	$ 401.5			$ 381.8			$ 1,210.6	$ 1,174.0
Nonoperating Income (Expense)	(52.5)			156.2			(181.8)	35.8
Provision for income taxes	66.4			180.6			214.4	328.1
Net earnings	221.0			319.0			597.6	725.7
Net Income (Loss) Attributable to Parent	$ 220.7	$ 190.4	$ 185.6	$ 318.8	$ 233.8	$ 173.2	$ 596.7	$ 725.8
Basic earnings per common share (in dollars per share)	$ 2.26			$ 3.14			$ 6.08	$ 7.13
Diluted earnings per common share (in dollars per share)	$ 2.25			$ 3.10			$ 6.04	$ 7.04
Net Cash Provided by (Used in) Investing Activities							$ (1,131.0)	$ 353.6
Net Cash Provided by (Used in) Financing Activities							196.7	(587.0)
Effect of exchange rate changes on cash and cash equivalents							(6.3)	(9.6)
Cash and Cash Equivalents, Period Increase (Decrease)							(65.7)	576.0
Assets	$ 17,847.8						17,847.8		16,185.3
Long-term debt, less current portion	2,554.9						2,554.9		1,878.9
Common stock, 92.8 and 93.5 shares outstanding at March 31, 2013 and December 31, 2012, respectively	19.7						19.7		19.1
Stockholders' Equity Attributable to Parent	7,231.1	$ 7,144.4	$ 7,111.3	$ 7,248.1	$ 7,037.7	$ 6,984.0	7,231.1	7,248.1	6,971.4	$ 6,804.1
Liabilities and Equity	17,847.8						17,847.8		16,185.3
Capitalized Contract Cost, Amortization	2.3			0.8			6.1	3.3
Deferred Revenue, Revenue Recognized							232.8	144.8
Revenue, Remaining Performance Obligation, Amount	4,310.7						$ 4,310.7
Contract with Customer, Performance Obligation Satisfied in Previous Period	67.7			20.5
Prior Period Reclassification Adjustment									$ 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	$ 1,759.2			$ 1,752.0			$ 5,242.1	$ 5,336.3
Percent of Revenue Contributed	60.00%			62.00%			61.00%	62.00%
Covance Drug Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revenues	$ 1,175.4			$ 1,081.5			$ 3,376.4	$ 3,214.1
Percent of Revenue Contributed	40.00%						39.00%