Document and Entity Information Document - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 22, 2018
Entity Information [Line Items]
Net sales	$ 2,701.5	$ 2,597.9	$ 2,498.4	$ 2,408.1	$ 2,387.3	$ 2,372.7	$ 2,382.0	$ 2,295.2	$ 10,205.9	$ 9,437.2	$ 8,505.7
Entity Registrant Name									LABORATORY CORP OF AMERICA HOLDINGS
Entity Central Index Key									0000920148
Current Fiscal Year End Date									--12-31
Entity Filer Category									Large Accelerated Filer
Document Type									10-K
Document Period End Date									Dec. 31, 2017
Document Fiscal Year Focus									2017
Document Fiscal Period Focus									FY
Amendment Flag									false
Entity Common Stock, Shares Outstanding												101.9
Entity Well-known Seasoned Issuer									Yes
Entity Voluntary Filers									No
Entity Current Reporting Status									Yes
Entity Public Float			$ 14,900.0
Genomic and Esoteric Testing [Member]
Entity Information [Line Items]
Net sales								$ 2,844.1			$ 2,306.4