BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended						9 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
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%			100.00%			100.00%	100.00%
Intercompany revenue elimination	$ (6.1)			$ (2.2)			$ (17.1)	$ (4.5)
Revenues	2,928.5			2,831.3			8,601.4	8,545.9
Operating Income (Loss)	339.9			343.4			993.8	1,018.0
Earnings before income taxes	287.4			499.6			812.0	1,053.8
Provision for income taxes	287.4			499.6			812.0	1,053.8
Provision for income taxes	66.4			180.6			214.4	328.1
Net earnings	221.0			319.0			597.6	725.7
Net income attributable to Laboratory Corporation of America Holdings	(0.3)			(0.2)			(0.9)	0.1
Nonoperating Income (Expense)	(52.5)			156.2			(181.8)	35.8
Net Income (Loss) Attributable to Parent	220.7	$ 190.4	$ 185.6	318.8	$ 233.8	$ 173.2	596.7	725.8
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (46.1)			$ (33.9)			$ (126.8)	$ (106.5)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	60.00%			62.00%			61.00%	62.00%
Revenues	$ 1,759.2			$ 1,752.0			$ 5,242.1	$ 5,336.3
Operating Income (Loss)	$ 262.2			289.4			$ 843.0	929.2
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	40.00%						39.00%
Revenues	$ 1,175.4			1,081.5			$ 3,376.4	3,214.1
Operating Income (Loss)	$ 123.8			$ 87.9			$ 277.6	$ 195.3