BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Total net revenues	$ 2,597.9	$ 2,372.7	$ 7,504.4	$ 7,049.9
Intercompany revenue elimination	(0.4)	(0.2)	(0.9)	(0.5)
Reimbursement Revenue	57.3	42.0	140.7	163.5
Revenues	2,655.2	2,414.7	7,645.1	7,213.4
Operating Income (Loss)	341.3	324.0	1,010.0	989.0
Earnings before income taxes	281.1	263.4	845.9	828.9
Provision for income taxes	281.1	263.4	845.9	828.9
Provision for income taxes	97.7	83.6	281.1	280.3
Net earnings	183.4	179.8	564.8	548.6
Net income attributable to Laboratory Corporation of America Holdings	(2.8)	(0.3)	(3.4)	(0.9)
Income Loss from Continuing Operations Before Income Taxes and Minority Interest	(60.2)	(60.6)	(164.1)	(160.1)
Net Income (Loss) Attributable to Parent	180.6	179.5	561.4	547.7
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (37.9)	(33.5)	$ (105.1)	(111.3)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	70.70%		71.30%
Total net revenues	$ 1,837.2	1,671.8	$ 5,354.2	4,922.1
Operating Income (Loss)	$ 336.2	305.6	980.2	$ 910.0
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	29.30%			28.70%
Total net revenues	$ 761.1	701.1	2,151.1	$ 2,128.3
Operating Income (Loss)	$ 43.0	$ 51.9	$ 134.9	$ 190.3