BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%	100.00%
Intercompany revenue elimination	$ (5.5)	$ (0.4)
Revenues	2,791.2	2,848.3
Operating Income (Loss)	318.2	305.4
Earnings before income taxes	254.7	241.5
Provision for income taxes	254.7	241.5
Provision for income taxes	68.8	69.0
Net earnings	185.9	172.5
Net income attributable to Laboratory Corporation of America Holdings	(0.3)	0.7
Nonoperating Income (Expense)	(63.5)	(63.9)
Net Income (Loss) Attributable to Parent	185.6	173.2
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (38.1)	$ (36.6)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	62.00%	62.00%
Revenues	$ 1,722.0	$ 1,770.2
Operating Income (Loss)	$ 268.3	303.4
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	38.00%
Revenues	$ 1,074.7	1,078.5
Operating Income (Loss)	$ 88.0	$ 38.6