Business Segments (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,718.6				$ 1,747.4					$ 1,718.6	$ 1,747.4
Depreciation and amortization:
Depreciation and amortization									$ 245.5	499.2	457.8
Depreciation and Amortization of Intangible Assets									234.3	490.5	434.3
Net revenues:
Net sales	2,387.3	$ 2,372.7	$ 2,382.0	$ 2,295.2	2,244.8	$ 2,269.9	$ 2,218.7	$ 1,772.3	6,011.6	9,437.2	8,505.7
Intercompany revenue elimination									0.0	(0.8)	0.0
Reimbursement Revenue									0.0	204.6	174.4	$ 0.0
Revenues									6,011.6	9,641.8	8,680.1	6,011.6
Operating Income (Loss)									904.3	1,312.4	996.8
Nonoperating Income (Expense)									(83.7)	(206.9)	(270.8)
Total pre-tax income									820.6	1,105.5	726.0
Provision for income taxes									308.0	372.3	287.3
Net earnings									512.6	733.2	438.7
Net Income (Loss) Attributable to Noncontrolling Interest									(1.4)	(1.1)	(1.1)
Net earnings attributable to Laboratory Corporation of America Holdings	184.4	$ 179.5	$ 204.1	$ 164.1	$ 110.0	$ 154.7	$ 169.9	$ 3.0	511.2	732.1	437.6
LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	831.9									831.9
Depreciation and amortization:
Depreciation and amortization									184.8	270.9	245.8
Net revenues:
Net sales									5,838.0	6,593.9	6,199.3
Operating Income (Loss)									976.2	1,187.6	1,053.7
Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	886.7									886.7
Depreciation and amortization:
Depreciation and amortization									5.3	219.5	184.4
Net revenues:
Net sales									173.6	2,844.1	2,306.4
Intercompany revenue elimination										(0.8)	0.0	$ 0.0
Operating Income (Loss)									40.7	272.7	73.5
Corporate Segment [Member]
Depreciation and amortization:
Depreciation and amortization									44.2	0.1	4.1
Net revenues:
Operating Income (Loss)									$ (112.6)	(147.9)	$ (130.4)
UNITED STATES
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,417.8									1,417.8
Net revenues:
Net sales										7,640.5
UNITED STATES | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	778.5									778.5
Net revenues:
Net sales										6,246.1
UNITED STATES | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	639.3									639.3
Net revenues:
Net sales										1,395.2
Intercompany revenue elimination										(0.8)
CANADA
Segment Reporting Information [Line Items]
Property, plant and equipment, net	50.1									50.1
Net revenues:
Net sales										295.8
CANADA | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	50.1									50.1
Net revenues:
Net sales										295.8
CANADA | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.0									0.0
Net revenues:
Net sales										0.0
Intercompany revenue elimination										0.0
UNITED KINGDOM
Segment Reporting Information [Line Items]
Property, plant and equipment, net	107.9									107.9
Net revenues:
Net sales										275.9
UNITED KINGDOM | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	2.4									2.4
Net revenues:
Net sales										41.8
UNITED KINGDOM | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	105.5									105.5
Net revenues:
Net sales										234.1
Intercompany revenue elimination										0.0
SWITZERLAND
Segment Reporting Information [Line Items]
Property, plant and equipment, net	81.4									81.4
Net revenues:
Net sales										450.5
SWITZERLAND | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.0									0.0
Net revenues:
Net sales										0.0
SWITZERLAND | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	81.4									81.4
Net revenues:
Net sales										450.5
Intercompany revenue elimination										0.0
Other countries [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	61.4									61.4
Net revenues:
Net sales										774.5
Other countries [Member] | LabCorp Diagnostics [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0.9									0.9
Net revenues:
Net sales										10.2
Other countries [Member] | Covance Drug Development [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 60.5									60.5
Net revenues:
Net sales										764.3
Intercompany revenue elimination										$ 0.0