Business Segments [Disclosure] (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 2,636.6				$ 1,740.3				$ 2,636.6	$ 1,740.3
Depreciation and amortization:
Depreciation and amortization									577.2	552.1	$ 533.2
Depreciation and Amortization of Intangible Assets									564.7	543.2	523.3
Intercompany revenue elimination									(23.4)	(10.5)	(1.8)
Revenues	2,953.4	$ 2,928.5	$ 2,881.7	$ 2,791.2	2,787.5	$ 2,831.3	$ 2,866.3	$ 2,848.3	11,554.8	11,333.4	10,308.0
Operating Income (Loss)	336.4	339.9	335.7	318.2	307.7	343.4	369.2	305.4	1,330.2	1,325.7	1,305.2
Nonoperating Income (Expense)									(225.3)	(57.4)	(227.7)
Total pre-tax income									1,104.9	1,268.3	1,077.5
Income Tax Expense (Benefit)									280.0	384.4	(155.4)
Net earnings									824.9	883.9	1,232.9
Net Income (Loss) Attributable to Noncontrolling Interest									(1.1)	(0.2)	(5.8)
Net earnings attributable to Laboratory Corporation of America Holdings	227.1	$ 220.7	$ 190.4	$ 185.6	$ 157.9	$ 318.8	$ 233.8	$ 173.2	823.8	883.7	1,227.1
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,480.0								1,480.0
Depreciation and amortization:
Depreciation and amortization									301.0	293.3	304.7
Revenues									7,000.1	7,030.8	6,858.2
Operating Income (Loss)									1,086.0	1,166.7	1,300.9
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,156.6								1,156.6
Depreciation and amortization:
Depreciation and amortization									261.1	247.3	217.4
Revenues									4,578.1	4,313.1	3,451.6
Operating Income (Loss)									411.5	303.6	144.9
Corporate Segment [Member]
Depreciation and amortization:
Depreciation and amortization									2.6	2.6	1.2
Operating Income (Loss)									(167.3)	$ (144.6)	$ (140.6)
UNITED STATES
Segment Reporting Information [Line Items]
Property, plant and equipment, net	2,079.9								2,079.9
Depreciation and amortization:
Revenues									8,981.0
UNITED STATES | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,385.1								1,385.1
Depreciation and amortization:
Revenues									6,662.6
UNITED STATES | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	694.8								694.8
Depreciation and amortization:
Revenues									2,341.8
CANADA
Segment Reporting Information [Line Items]
Property, plant and equipment, net	94.9								94.9
Depreciation and amortization:
Intercompany revenue elimination									0.0
Revenues									333.3
CANADA | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	94.9								94.9
Depreciation and amortization:
Revenues									333.3
CANADA | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.0								0.0
Depreciation and amortization:
Revenues									0.0
UNITED KINGDOM
Segment Reporting Information [Line Items]
Property, plant and equipment, net	196.2								196.2
Depreciation and amortization:
Intercompany revenue elimination									0.0
Revenues									507.9
UNITED KINGDOM | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.0								0.0
Depreciation and amortization:
Revenues									0.0
UNITED KINGDOM | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	196.2								196.2
Depreciation and amortization:
Revenues									507.9
SWITZERLAND
Segment Reporting Information [Line Items]
Property, plant and equipment, net	92.9								92.9
Depreciation and amortization:
Intercompany revenue elimination									0.0
Revenues									532.9
SWITZERLAND | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.0								0.0
Depreciation and amortization:
Revenues									0.0
SWITZERLAND | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	92.9								92.9
Depreciation and amortization:
Revenues									532.9
Other countries [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	172.7								172.7
Depreciation and amortization:
Intercompany revenue elimination									0.0
Revenues									1,199.7
Other countries [Member] | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.0								0.0
Depreciation and amortization:
Revenues									4.2
Other countries [Member] | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 172.7								172.7
Depreciation and amortization:
Revenues									$ 1,195.5