EARNINGS PER SHARE (Reconciliation of Basic Earnings Per Share to Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income [Abstract]
Net earnings attributable to Laboratory Corporation of America Holdings	$ 185.6	$ 173.2
Shares [Abstract]
Net earnings, basic (in shares)	98.6	101.9
Dilutive effect of employee stock options and awards, (in shares)	0.9	1.5
Per Share Amount [Abstract]
Basic earnings per common share (in dollars per share)	$ 1.88	$ 1.70
Diluted earnings per common share (in dollars per share)	$ 1.86	$ 1.67
Net Income (Loss) Available to Common Stockholders, Diluted	$ 185.6	$ 173.2
Weighted Average Number of Shares Outstanding, Diluted	99.5	103.4