BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%	100.00%	100.00%	100.00%
Intercompany revenue elimination	$ (1.9)	$ (0.4)	$ (2.2)	$ (0.6)
Revenues	2,866.3	2,528.2	5,714.6	4,941.9
Operating Income (Loss)	369.2	329.8	674.6	647.9
Earnings before income taxes	312.7	279.2	554.2	544.4
Provision for income taxes	312.7	279.2	554.2	544.4
Provision for income taxes	78.6	94.1	147.6	176.0
Net earnings	234.1	185.1	406.6	368.4
Net income attributable to Laboratory Corporation of America Holdings	(0.3)	(0.3)	0.4	(0.6)
Nonoperating Income (Expense)	(56.5)	(50.6)	(120.4)	(103.5)
Net Income (Loss) Attributable to Parent	233.8	184.8	407.0	367.8
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (35.9)	$ (34.3)	$ (72.5)	$ (67.2)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	63.00%	68.00%	63.00%	68.00%
Revenues	$ 1,814.0	$ 1,721.1	$ 3,584.2	$ 3,360.8
Operating Income (Loss)	$ 336.3	334.5	$ 639.8	644.0
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	37.00%		37.00%
Revenues	$ 1,054.2	807.5	$ 2,132.6	1,581.7
Operating Income (Loss)	$ 68.8	$ 29.6	$ 107.3	$ 71.1