BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%	100.00%
Intercompany revenue elimination	$ (22.0)	$ (5.5)
Revenues	2,823.8	2,791.2
Operating Income (Loss)	(192.6)	318.2
Earnings before income taxes	(267.7)	254.7
Provision for income taxes	(267.7)	254.7
Provision for income taxes	49.2	68.8
Net earnings	(316.9)	185.9
Net income attributable to Laboratory Corporation of America Holdings	(0.3)	(0.3)
Nonoperating Income (Expense)	(75.1)	(63.5)
Net Income (Loss) Attributable to Parent	(317.2)	185.6
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (42.3)	$ (38.1)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	60.00%	62.00%
Revenues	$ 1,702.0	$ 1,722.0
Operating Income (Loss)	$ 188.4	268.3
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	40.00%
Revenues	$ 1,143.8	1,074.7
Operating Income (Loss)	$ (338.7)	$ 88.0