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				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Income [Abstract]
Net earnings attributable to Laboratory Corporation of America Holdings	$ 358.6	$ 491.6	$ 467.4	$ 769.6	$ 850.2	$ 1,237.0
Shares [Abstract]
Net earnings, basic (in shares)	92.3		97.4		92.7	97.5
Dilutive effect of employee stock options and awards, (in shares)	0.4		0.8		0.6	0.8
Per Share Amount [Abstract]
Basic earnings per common share (in dollars per share)	$ 3.89		$ 4.80		$ 9.17	$ 12.69
Diluted earnings per common share (in dollars per share)	$ 3.87		$ 4.76		$ 9.11	$ 12.58
Net Income (Loss) Available to Common Stockholders, Diluted	$ 358.6		$ 467.4		$ 850.2	$ 1,237.0
Weighted Average Number of Shares Outstanding, Diluted	92.7		98.2		93.3	98.4