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, 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	173.2			173.2
Other comprehensive earnings, net of tax	52.5					52.5
Issuance of common stock under employee stock plans	28.4	0.0	28.4
Surrender of restricted stock and performance share awards	(25.0)				(25.0)
Conversion of zero-coupon convertible debt	0.0		0.0		0.0
Stock compensation	25.8		25.8
Purchase of common stock	(75.0)	0.0	75.0
BALANCE at Mar. 31, 2018	6,984.0	12.0	1,969.0	6,369.3	(1,085.1)	(281.2)
BALANCE at Dec. 31, 2018	6,971.4	11.7	1,451.1	7,079.8	(1,108.1)	(463.1)
Net earnings attributable to Laboratory Corporation of America Holdings	185.6			185.6
Other comprehensive earnings, net of tax	23.6			0.0		23.6
Other Significant Noncash Transaction, Value of Consideration Given	24.7
Issuance of common stock under employee stock plans	19.4	0.0	24.7
Surrender of restricted stock and performance share awards					(19.4)
Conversion of zero-coupon convertible debt	0.0		0.0
Stock compensation	25.5		25.5
Purchase of common stock	(100.1)	0.1	100.0
BALANCE at Mar. 31, 2019	$ 7,111.3	$ 11.6	$ 1,401.3	$ 7,265.4	$ (1,127.5)	$ (439.5)