QUARTERLY DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Prior Period Reclassification Adjustment	$ 57.9	$ (102.8)	$ 33.4	$ (167.7)	$ 138.3	$ (207.5)	$ 149.0	$ (289.9)
Summary of unaudited quarterly data
Net sales	2,387.3	2,372.7	2,382.0	2,295.2	2,244.8	2,269.9	2,218.7	1,772.3	$ 6,011.6	$ 9,437.2	$ 8,505.7
Cost of Goods and Services Sold									3,808.5	6,256.7	5,602.4
Gross profit	788.0	788.4	826.8	777.3	740.7	764.9	772.6	625.1	2,203.1	3,180.5	2,903.3
Net earnings attributable to Laboratory Corporation of America Holdings	$ 184.4	$ 179.5	$ 204.1	$ 164.1	$ 110.0	$ 154.7	$ 169.9	$ 3.0	$ 511.2	$ 732.1	$ 437.6
Earnings Per Share
Basic earnings per share (in dollars per share)	$ 1.79	$ 1.74	$ 2.00	$ 1.62	$ 1.09	$ 1.53	$ 1.69	$ 0.04	$ 6.03	$ 7.14	$ 4.43
Diluted earnings per common share (in dollars per share)	$ 1.75	$ 1.71	$ 1.96	$ 1.58	$ 1.07	$ 1.51	$ 1.66	$ 0.04	$ 5.91	$ 7.02	$ 4.35
Covance, Inc. [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax								$ 122.2