Document and Entity Information Document - shares shares in Millions	9 Months Ended
	Sep. 30, 2018	Oct. 26, 2018
Document Information [Line Items]
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-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		100.9
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes