CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Common Stock [Member] Revision of Prior Period, Accounting Standards Update, Adjustment	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Revision of Prior Period, Accounting Standards Update, Adjustment	Retained Earnings [Member]	Retained Earnings [Member] Revision of Prior Period, Accounting Standards Update, Adjustment	Treasury Stock [Member]	Treasury Stock [Member] Revision of Prior Period, Accounting Standards Update, Adjustment	Accumulated Other Comprehensive Income [Member]	Accumulated Other Comprehensive Income [Member] Revision of Prior Period, Accounting Standards Update, Adjustment
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	0.0		0.0		185.6		0.0		0.0
Other comprehensive earnings, net of tax	23.6	0.0		0.0		0.0		0.0		23.6
Issuance of common stock under employee stock plans	(24.7)	0.0		(24.7)		0.0		0.0		0.0
Surrender of restricted stock and performance share awards	(19.4)	0.0		0.0		0.0		(19.4)		0.0
Stock compensation	25.5	0.0		25.5		0.0		0.0		0.0
Purchase of common stock	(100.1)	0.1		100.0		0.0		0.0		0.0
BALANCE at Mar. 31, 2019	7,111.3	11.6		1,401.3		7,265.4		(1,127.5)		(439.5)
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	376.0
Other comprehensive earnings, net of tax	51.2
Conversion of zero-coupon convertible debt	7.2
BALANCE at Jun. 30, 2019	7,144.4	9.1		91.4		7,455.8		0.0		(411.9)
BALANCE at Mar. 31, 2019	7,111.3	11.6		1,401.3		7,265.4		(1,127.5)		(439.5)
Net earnings attributable to Laboratory Corporation of America Holdings	190.4	0.0		0.0		190.4		0.0		0.0
Other comprehensive earnings, net of tax	27.6	0.0		0.0		0.0		0.0		27.6
Issuance of common stock under employee stock plans	(9.2)	0.0		(9.2)		0.0		0.0		0.0
Surrender of restricted stock and performance share awards	(20.7)	0.0		0.0		0.0		(20.7)		0.0
Stock compensation	26.5	0.0		26.5		0.0		0.0		0.0
Purchase of common stock	(199.9)	0.1		199.8		0.0		0.0		0.0
BALANCE at Jun. 30, 2019	7,144.4	9.1		91.4		7,455.8		0.0		(411.9)
Treasury Stock, Retired, Cost Method, Amount	0.0	(2.4)		(1,145.8)		0.0		(1,148.2)		0.0
Retained Earnings (Accumulated Deficit)	7,903.6
BALANCE at Dec. 31, 2019	7,567.0	9.0		26.8		7,903.6		0.0		(372.4)
Net earnings attributable to Laboratory Corporation of America Holdings	(317.2)	0.0		0.0		(317.2)		0.0		0.0
Other comprehensive earnings, net of tax	(145.5)	0.0		0.0		0.0		0.0		(145.5)
Issuance of common stock under employee stock plans	(26.9)	0.0		(26.9)		0.0		0.0		0.0
Surrender of restricted stock and performance share awards	(22.0)	0.0		(22.0)		0.0		0.0		0.0
Stock compensation	17.9	0.0		17.9		0.0		0.0		0.0
Purchase of common stock	(100.0)	0.0		49.6		50.4		0.0		0.0
BALANCE at Mar. 31, 2020	7,020.1	9.0		0.0		7,529.0		0.0		(517.9)
BALANCE at Dec. 31, 2019	7,567.0	9.0		26.8		7,903.6		0.0		(372.4)
Net earnings attributable to Laboratory Corporation of America Holdings	(85.6)
Other comprehensive earnings, net of tax	(76.6)
Conversion of zero-coupon convertible debt	0.0
BALANCE at Jun. 30, 2020	7,352.7	9.0		32.1		7,760.6		0.0		(449.0)
Retained Earnings (Accumulated Deficit)			$ 0.0		$ 0.0		$ (7.0)		$ 0.0		$ 0.0
BALANCE at Mar. 31, 2020	7,020.1	9.0		0.0		7,529.0		0.0		(517.9)
Net earnings attributable to Laboratory Corporation of America Holdings	231.6	0.0		0.0		231.6		0.0		0.0
Other comprehensive earnings, net of tax	68.9	0.0		0.0		0.0		0.0		68.9
Issuance of common stock under employee stock plans	(1.8)	0.0		(1.8)		0.0		0.0		0.0
Surrender of restricted stock and performance share awards	(9.5)	0.0		(9.5)		0.0		0.0		0.0
Stock compensation	39.8	0.0		39.8		0.0		0.0		0.0
Purchase of common stock	0.0	0.0		0.0		0.0		0.0		0.0
BALANCE at Jun. 30, 2020	7,352.7	$ 9.0		$ 32.1		$ 7,760.6		$ 0.0		$ (449.0)
Retained Earnings (Accumulated Deficit)	$ 7,760.6