Business Segments [Disclosure] (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 2,729,600,000	$ 2,636,600,000
Depreciation and amortization:
Depreciation and amortization	624,700,000	577,200,000	$ 552,100,000
Depreciation and Amortization of Intangible Assets	624,700,000	564,700,000	543,200,000
Intercompany revenue elimination	(152,600,000)
Revenues	13,978,500,000	11,554,800,000	11,333,400,000
Operating Income (Loss)	2,445,400,000	1,330,200,000	1,325,700,000
Nonoperating Income (Expense)	(226,300,000)	(225,300,000)	(57,400,000)
Total pre-tax income	2,219,100,000	1,104,900,000	1,268,300,000
Income Tax Expense (Benefit)	662,100,000	280,000,000.0	384,400,000
Net earnings	1,557,000,000.0	824,900,000	883,900,000
Net Income (Loss) Attributable to Noncontrolling Interest	(900,000)	(1,100,000)	(200,000)
Net earnings attributable to Laboratory Corporation of America Holdings	1,556,100,000	823,800,000	883,700,000
Intersegment Eliminations
Depreciation and amortization:
Intercompany revenue elimination	(152,600,000)	(23,400,000)	(10,500,000)
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,515,300,000
Depreciation and amortization:
Depreciation and amortization	327,500,000	301,000,000.0	293,300,000
Operating Income (Loss)	2,634,900,000	1,086,000,000.0	1,166,700,000
Segment revenues	9,253,400,000	7,000,100,000	7,030,800,000
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,214,300,000
Depreciation and amortization:
Depreciation and amortization	295,200,000	261,100,000	247,300,000
Operating Income (Loss)	37,300,000	411,500,000	303,600,000
Segment revenues	4,877,700,000	4,578,100,000	4,313,100,000
Corporate Segment [Member]
Depreciation and amortization:
Depreciation and amortization	2,000,000	2,600,000	2,600,000
Operating Income (Loss)	(226,800,000)	$ (167,300,000)	$ (144,600,000)
Other countries [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	123,500,000
Depreciation and amortization:
Intercompany revenue elimination	0
Revenues	941,000,000.0
Other countries [Member] | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0
Depreciation and amortization:
Segment revenues	0
Other countries [Member] | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	123,500,000
Depreciation and amortization:
Segment revenues	941,000,000.0
North America
Segment Reporting Information [Line Items]
Property, plant and equipment, net	2,180,600,000
Depreciation and amortization:
Revenues	11,525,300,000
North America | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,515,300,000
Depreciation and amortization:
Segment revenues	9,253,400,000
North America | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	665,300,000
Depreciation and amortization:
Segment revenues	2,424,500,000
Europe [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	425,500,000
Depreciation and amortization:
Intercompany revenue elimination	0
Revenues	1,512,200,000
Europe [Member] | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0
Depreciation and amortization:
Segment revenues	0
Europe [Member] | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	425,500,000
Depreciation and amortization:
Segment revenues	$ 1,512,200,000