BUSINESS SEGMENT INFORMATION Business Segment Information (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	100.00%			100.00%			100.00%	100.00%
Intercompany revenue elimination	$ (50,000,000.0)			$ (6,200,000)			$ (90,000,000.0)	$ (17,100,000)
Revenues	3,896,100,000			2,928,500,000			9,488,700,000	8,601,400,000
Operating Income (Loss)	1,047,100,000			339,900,000			1,152,200,000	993,800,000
Earnings before income taxes	947,100,000			287,400,000			976,400,000	812,000,000.0
Provision for income taxes	243,400,000			66,400,000			358,000,000.0	214,400,000
Net earnings	703,700,000			221,000,000.0			618,400,000	597,600,000
Net income attributable to Laboratory Corporation of America Holdings	(300,000)			(300,000)			(600,000)	(900,000)
Nonoperating Income (Expense)	(100,000,000.0)			(52,500,000)			(175,700,000)	(181,800,000)
Net Income (Loss) Attributable to Parent	703,400,000	$ 231,600,000	$ (317,200,000)	$ 220,700,000	$ 190,400,000	$ 185,600,000	$ 617,800,000	$ 596,700,000
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (59,800,000)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	68.00%			60.00%			63.00%	61.00%
Revenues	$ 2,704,200,000			$ 1,759,200,000			$ 6,098,800,000	$ 5,242,100,000
Operating Income (Loss)	$ 964,900,000			262,200,000			$ 1,451,500,000	843,000,000.0
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Percent of Revenue Contributed	32.00%						37.00%
Revenues	$ 1,241,900,000			1,175,400,000			$ 3,479,400,000	3,376,400,000
Operating Income (Loss)	$ 142,000,000.0			123,800,000			(131,200,000)	277,600,000
Corporation
Segment Reporting Information [Line Items]
Operating Income (Loss)				$ (46,100,000)			$ (168,200,000)	$ (126,800,000)