QUARTERLY DATA (UNAUDITED) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of unaudited quarterly data
Net sales	$ 1,366.1	$ 1,404.5	$ 1,403.3	$ 1,368.4	$ 1,295.4	$ 1,276.5	$ 1,238.4	$ 1,193.6	$ 5,542.3	$ 5,003.9	$ 4,694.7
Gross profit	549.6	568.5	588.2	568.4	529.6	527.7	533.6	506.9	2,274.7	2,097.8	1,970.9
Net earnings attributable to Laboratory Corporation of America Holdings	$ 135.4	$ 134.3	$ 122.9	$ 127.1	$ 131.8	$ 140.0	$ 153.7	$ 132.7	$ 519.7	$ 558.2	$ 543.3
Earnings Per Share
Basic earnings per share (in dollars per share)	$ 1.36	$ 1.34	$ 1.22	$ 1.27	$ 1.29	$ 1.37	$ 1.48	$ 1.27	$ 5.20	$ 5.42	$ 5.06
Diluted earnings per common share (in dollars per share)	$ 1.34	$ 1.31	$ 1.20	$ 1.23	$ 1.26	$ 1.34	$ 1.46	$ 1.25	$ 5.11	$ 5.29	$ 4.98