BUSINESS SEGMENT INFORMATION Business Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Total net revenues	$ 1,468.2		$ 1,423.4		$ 2,909.1	$ 2,846.7
Total operating income	269.3		276.0		531.3	563.1
Non-operating expenses, net	19.3		19.8		39.9	37.3
Earnings before income taxes	250.0		256.2		491.4	525.8
Provision for income taxes	97.7		102.4		191.4	210.0
Net earnings	152.3		153.8		300.0	315.8
Less income attributable to noncontrolling interests	(0.4)		(0.5)		(0.8)	(0.9)
Net income attributable to Laboratory Corporation of America Holdings	151.9	151.9	153.3	153.3	299.2	314.9
Clinical diagnostics laboratory [Member]
Segment Reporting Information [Line Items]
Total net revenues	1,381.6		1,339.6		2,735.6	2,680.1
Total operating income	380.1		380.5		754.3	767.6
General corporate expenses [Member]
Segment Reporting Information [Line Items]
Total operating income	(134.0)		(130.3)		(270.7)	(256.3)
Other [Member]
Segment Reporting Information [Line Items]
Total net revenues	86.6		83.8		173.5	166.6
Total operating income	$ 23.2		$ 25.8		$ 47.7	$ 51.8