BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%		100.00%		100.00%	100.00%
Intercompany revenue elimination	$ (5.5)		$ (1.9)		$ (11.0)	$ (2.2)
Revenues	2,881.7		2,866.3		5,672.9	5,714.6
Operating Income (Loss)	335.7		369.2		653.9	674.6
Earnings before income taxes	270.0		312.7		524.7	554.2
Provision for income taxes	270.0		312.7		524.7	554.2
Provision for income taxes	79.3		78.6		148.1	147.6
Net earnings	190.7		234.1		376.6	406.6
Net income attributable to Laboratory Corporation of America Holdings	(0.3)		(0.3)		(0.6)	0.4
Nonoperating Income (Expense)	(65.7)		(56.5)		(129.2)	(120.4)
Net Income (Loss) Attributable to Parent	190.4	$ 185.6	233.8	$ 173.2	376.0	407.0
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (42.6)		$ (35.9)		$ (80.7)	$ (72.5)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	61.00%		63.00%		61.00%	62.00%
Revenues	$ 1,760.9		$ 1,814.0		$ 3,482.9	$ 3,584.2
Operating Income (Loss)	$ 312.5		336.3		$ 580.8	639.8
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	39.00%				39.00%
Revenues	$ 1,126.3		1,054.2		$ 2,201.0	2,132.6
Operating Income (Loss)	$ 65.8		$ 68.8		$ 153.8	$ 107.3