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, 2020	Mar. 31, 2019
Income [Abstract]
Net earnings attributable to Laboratory Corporation of America Holdings	$ (317.2)	$ 185.6
Shares [Abstract]
Net earnings, basic (in shares)	97.2	98.6
Dilutive effect of employee stock options and awards, (in shares)	0.0	0.9
Per Share Amount [Abstract]
Basic earnings per common share (in dollars per share)	$ (3.27)	$ 1.88
Diluted earnings per common share (in dollars per share)	$ (3.27)	$ 1.86
Net Income (Loss) Available to Common Stockholders, Diluted	$ (317.2)	$ 185.6
Weighted Average Number of Shares Outstanding, Diluted	97.2	99.5