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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income [Abstract]
Net earnings attributable to Laboratory Corporation of America Holdings	$ 179.5	$ 154.7	$ 547.7	$ 327.6
Net earnings including impact of dilutive adjustments	$ 179.5	$ 154.7	$ 547.7	$ 327.6
Shares [Abstract]
Net earnings, basic (in shares)		101.1	102.3	97.9
Dilutive effect of employee stock options and awards, (in shares)	1.5	1.2	1.4	1.2
Effect of convertible debt, net of tax, (in shares)	0.5	0.6	0.5	0.6
Net earnings including impact of dilutive adjustments, (in shares)	104.9	102.9	104.2	99.7
Per Share Amount [Abstract]
Basic earnings per common share (in dollars per share)	$ 1.74	$ 1.53	$ 5.36	$ 3.35
Diluted earnings per common share (in dollars per share)	$ 1.71	$ 1.50	$ 5.25	$ 3.29