SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - NET SALES (Details) - USD ($) $ 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	Dec. 31, 2014
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
Intercompany revenue elimination									0.0	(0.8)	0.0
Revenues									6,011.6	9,641.8	8,680.1	$ 6,011.6
Reimbursement Revenue									0.0	$ 204.6	$ 174.4	0.0
LabCorp Diagnostics [Member]
Percent of Revenue Contributed										69.90%	72.90%
Net sales									5,838.0	$ 6,593.9	$ 6,199.3
Clinical diagnostics laboratory [Member]
Net sales										$ 6,593.9
Routine Testing [Member]
Net sales											6,199.3	5,838.0
Genomic and Esoteric Testing [Member]
Net sales											$ 2,306.4	173.6
Covance Drug Development [Member]
Percent of Revenue Contributed										30.10%	27.10%
Net sales									$ 173.6	$ 2,844.1	$ 2,306.4
Intercompany revenue elimination										(0.8)	$ 0.0	$ 0.0
Other Segments [Member]
Net sales										$ 2,844.1