BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%	100.00%
Intercompany revenue elimination	$ (0.4)	$ (0.2)
Revenues	2,848.3	2,413.7
Operating Income (Loss)	305.4	318.1
Earnings before income taxes	241.5	265.3
Provision for income taxes	241.5	265.3
Provision for income taxes	69.0	82.0
Net earnings	172.5	183.3
Net income attributable to Laboratory Corporation of America Holdings	0.7	(0.3)
Nonoperating Income (Expense)	(63.9)	(52.8)
Net Income (Loss) Attributable to Parent	173.2	183.0
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (36.6)	$ (32.9)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	62.10%	67.90%
Total net revenues		$ 1,639.7
Revenues	$ 1,770.2
Operating Income (Loss)	$ 303.4	$ 309.5
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	37.90%	32.10%
Total net revenues		$ 774.2
Revenues	$ 1,078.5
Operating Income (Loss)	$ 38.6	$ 41.5