CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income [Member]
BALANCE at Dec. 31, 2016	$ 5,518.2	$ 12.1	$ 2,131.7	$ 4,969.0	$ (1,012.7)	$ (581.9)
Net earnings attributable to Laboratory Corporation of America Holdings	367.8			367.8
Other comprehensive earnings, net of tax	196.1					196.1
Issuance of common stock under employee stock plans	31.4	0.1	31.3
Surrender of restricted stock and performance share awards	(46.2)				(46.2)
Conversion of zero-coupon convertible debt	12.8		12.8		0.0
Stock compensation	52.7		52.7
Purchase of common stock	(256.0)	0.2	255.8
BALANCE at Jun. 30, 2017	5,876.8	12.0	1,972.7	5,336.8	(1,058.9)	(385.8)
BALANCE at Dec. 31, 2017	6,804.1	12.0	1,989.8	6,196.1	(1,060.1)	(333.7)
Net earnings attributable to Laboratory Corporation of America Holdings	407.0			407.0
Other comprehensive earnings, net of tax	(73.3)			0.0		(73.3)
Other Significant Noncash Transaction, Value of Consideration Given	43.0
Issuance of common stock under employee stock plans	45.1	0.0	43.0
Surrender of restricted stock and performance share awards					(45.1)
Stock compensation	52.0		52.0
Purchase of common stock	(150.0)	0.0	150.0
BALANCE at Jun. 30, 2018	$ 7,037.7	$ 12.0	$ 1,934.8	$ 6,603.1	$ (1,105.2)	$ (407.0)