CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income [Member]
BALANCE at Dec. 31, 2018	$ 6,971,400,000	$ 11,700,000	$ 1,451,100,000	$ 7,079,800,000	$ (1,108,100,000)	$ (463,100,000)
Net earnings attributable to Laboratory Corporation of America Holdings	185,600,000	0	0	185,600,000	0	0
Other comprehensive earnings, net of tax	23,600,000	0	0	0	0	23,600,000
Issuance of common stock under employee stock plans	(24,700,000)	0	(24,700,000)	0	0	0
Surrender of restricted stock and performance share awards	(19,400,000)	0	0	0	(19,400,000)	0
Stock compensation	25,500,000	0	25,500,000	0	0	0
Purchase of common stock	(100,100,000)	100,000	100,000,000.0	0	0	0
BALANCE at Mar. 31, 2019	7,111,300,000	11,600,000	1,401,300,000	7,265,400,000	(1,127,500,000)	(439,500,000)
BALANCE at Dec. 31, 2018	6,971,400,000	11,700,000	1,451,100,000	7,079,800,000	(1,108,100,000)	(463,100,000)
Net earnings attributable to Laboratory Corporation of America Holdings	596,700,000
Other comprehensive earnings, net of tax	(39,100,000)
Conversion of zero-coupon convertible debt	1,700,000
BALANCE at Sep. 30, 2019	7,231,100,000	9,000,000.0	47,800,000	7,676,500,000	0	(502,200,000)
BALANCE at Mar. 31, 2019	7,111,300,000	11,600,000	1,401,300,000	7,265,400,000	(1,127,500,000)	(439,500,000)
Net earnings attributable to Laboratory Corporation of America Holdings	190,400,000	0	0	190,400,000	0	0
Other comprehensive earnings, net of tax	27,600,000	0	0	0	0	27,600,000
Issuance of common stock under employee stock plans	(9,200,000)	0	(9,200,000)	0	0	0
Surrender of restricted stock and performance share awards	(20,700,000)	0	0	0	(20,700,000)	0
Stock compensation	26,500,000	0	26,500,000	0	0	0
Purchase of common stock	(199,900,000)	100,000	199,800,000	0	0	0
BALANCE at Jun. 30, 2019	7,144,400,000	9,100,000	91,400,000	7,455,800,000	0	(411,900,000)
Treasury Stock, Retired, Cost Method, Amount	0	(2,400,000)	(1,145,800,000)	0	(1,148,200,000)	0
Net earnings attributable to Laboratory Corporation of America Holdings	220,700,000	0	0		0	0
Other comprehensive earnings, net of tax	(90,300,000)	0	0	0	0
Issuance of common stock under employee stock plans	(25,100,000)	0	(25,100,000)	0	0	0
Surrender of restricted stock and performance share awards	(300,000)	0	(300,000)	0	0	0
Stock compensation	31,500,000	0	31,500,000	0	0	0
Purchase of common stock	(100,000,000.0)	100,000		0	0	0
BALANCE at Sep. 30, 2019	7,231,100,000	9,000,000.0	47,800,000	7,676,500,000	0	(502,200,000)
Treasury Stock, Retired, Cost Method, Amount			(99,900,000)
Retained Earnings (Accumulated Deficit)	7,903,600,000
BALANCE at Dec. 31, 2019	7,567,000,000.0	9,000,000.0	26,800,000	7,903,600,000	0	(372,400,000)
Net earnings attributable to Laboratory Corporation of America Holdings	(317,200,000)	0	0	(317,200,000)	0	0
Other comprehensive earnings, net of tax	(145,500,000)	0	0	0	0	(145,500,000)
Issuance of common stock under employee stock plans	(26,900,000)	0	(26,900,000)	0	0	0
Surrender of restricted stock and performance share awards	(22,000,000.0)	0	(22,000,000.0)	0	0	0
Stock compensation	17,900,000	0	17,900,000	0	0	0
Purchase of common stock	(100,000,000.0)	0	49,600,000	50,400,000	0	0
BALANCE at Mar. 31, 2020	7,020,100,000	9,000,000.0	0	7,529,000,000.0	0	(517,900,000)
BALANCE at Dec. 31, 2019	7,567,000,000.0	9,000,000.0	26,800,000	7,903,600,000	0	(372,400,000)
Net earnings attributable to Laboratory Corporation of America Holdings	617,800,000
Other comprehensive earnings, net of tax	57,800,000
Conversion of zero-coupon convertible debt	0
BALANCE at Sep. 30, 2020	8,239,100,000	9,000,000.0	80,700,000	8,464,000,000.0	0	(314,600,000)
BALANCE at Mar. 31, 2020	7,020,100,000	9,000,000.0	0	7,529,000,000.0	0	(517,900,000)
Net earnings attributable to Laboratory Corporation of America Holdings	231,600,000	0	0	231,600,000	0	0
Other comprehensive earnings, net of tax	68,900,000	0	0	0	0	68,900,000
Issuance of common stock under employee stock plans	(1,800,000)	0	(1,800,000)	0	0	0
Surrender of restricted stock and performance share awards	(9,500,000)	0	(9,500,000)	0	0	0
Stock compensation	39,800,000	0	39,800,000	0	0	0
BALANCE at Jun. 30, 2020	7,352,700,000	9,000,000.0	32,100,000	7,760,600,000	0	(449,000,000.0)
Net earnings attributable to Laboratory Corporation of America Holdings	703,400,000	0	0	703,400,000	0	0
Other comprehensive earnings, net of tax	134,400,000	0	0	0	0	134,400,000
Issuance of common stock under employee stock plans	(21,900,000)	0	(21,900,000)	0	0	0
Surrender of restricted stock and performance share awards	(500,000)	0	(500,000)	0	0	0
Stock compensation	27,200,000	0	27,200,000	0	0	0
BALANCE at Sep. 30, 2020	8,239,100,000	$ 9,000,000.0	$ 80,700,000	$ 8,464,000,000.0	$ 0	$ (314,600,000)
Retained Earnings (Accumulated Deficit)	$ 8,464,000,000.0