BUSINESS ACQUISITIONS (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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	Dec. 31, 2013	Jul. 27, 2016	Feb. 19, 2015	Jan. 30, 2015	Dec. 19, 2014	Nov. 20, 2014	Nov. 01, 2013
Business Acquisition [Line Items]
Cash paid for acquisition															$ 1,762.5
Non-cash consideration															4,388.2
Stock Issued During Period, Shares, Acquisitions										15.3
Total acquisition consideration (cash and non-cash)					$ 0.0						$ 0.0			$ 249.1	6,150.7
Long-term debt, less current portion	$ 5,300.0				5,940.3					$ 5,300.0	5,940.3
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability									$ 10.4	4.9	1.7
Employee Severance Benefits Related Restructuring Reserve Accrual Adjustment										2.8			$ 0.4
Facility Related Restructuring Reserve Accrual Adjustment										3.5	1.1		$ 0.7
Business Acquisition, Share Price														$ 2.40
Cost of Acquired Entity [Abstract]
Goodwill, net	6,424.4				6,202.1					6,424.4	6,202.1	$ 3,099.4
Payments to Acquire Businesses, Net of Cash Acquired									159.4	548.6	3,736.0	91.5
Finite-lived Intangible Assets Acquired										272.8
Goodwill, Acquired During Period										$ 398.3	3,115.5
Line of Credit Facility, Maximum Borrowing Capacity																	$ 1,000.0
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										15 years 2 months
Cash payments to acquire laboratory-related assets									203.5	$ 278.9	255.8
Senior Notes, Noncurrent	2,900.0									2,900.0						$ 2,900.0			$ 700.0
Noncontrolling Interest Put [Abstract]
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
Proforma consolidated net revenue											2,209.7
Proforma consolidated net income											167.2
Unbilled Receivables, Current	97.1				92.5					97.1	92.5
Revenues									6,011.6	9,641.8	8,680.1	$ 6,011.6
Operating Income (Loss)									904.3	1,312.4	996.8
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
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents					0.0						0.0				780.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables					0.0						0.0				334.8
Business Combination, Contingent Consideration, Asset, Current					0.0						0.0				138.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory					0.0						0.0				51.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets					86.5						86.5				347.9
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets					87.1						87.1				121.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment					174.0						174.0				1,018.2
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net					(108.0)						(108.0)				(3,068.1)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets					(3.2)						(3.2)				(12.0)
Business Combination, Separately Recognized Transactions, Assets Recognized					205.7						205.7				8,054.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable					0.0						0.0				190.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities					26.1						26.1				306.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue					0.0						0.0				168.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities, Current					149.1						149.1				879.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt					0.0						0.0				250.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other					30.5						30.5				109.0
Business Combination, Separately Recognized Transactions, Liabilities Recognized					205.7						205.7				1,904.0
Senior notes due 2025 [Member]
Purchase Price Allocation [Abstract]
Debt Instrument, Interest Rate, Stated Percentage																3.60%
Senior Notes, Noncurrent																$ 1,000.0
Senior notes due 2020 [Member]
Business Acquisition [Line Items]
Long-term debt, less current portion	600.0									600.0
Sequenom acquisition [Member]
Cost of Acquired Entity [Abstract]
Business combination, recognized identifiable deferred tax liabilities assumed	45.1									45.1
Finite-lived Intangible Assets Acquired										146.6
Goodwill, Acquired During Period										$ 206.0
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										14 years 7 months
Excluding Covance [Member]
Cost of Acquired Entity [Abstract]
Payments to Acquire Businesses, Net of Cash Acquired											$ 299.5
Finite-lived Intangible Assets Acquired										$ 126.2
Goodwill, Acquired During Period										192.3
LipoScience [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price																		$ 5.25
Cost of Acquired Entity [Abstract]
Business combination, recognized identifiable intangible assets acquired																		$ 27.2
Business combination, recognized identifiable deferred tax liabilities assumed																		9.4
Goodwill, net																		$ 17.4
Payments to Acquire Businesses, Net of Cash Acquired					67.9
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets											19 years 6 months
Acquisitions excluding LipoScience [Member]
Cost of Acquired Entity [Abstract]
Payments to Acquire Businesses, Net of Cash Acquired											$ 128.4
Finite-lived Intangible Assets Acquired											17.4
Goodwill, Acquired During Period											68.4
Covance [Member]
Business Acquisition [Line Items]
Cash on Hand Used for Acquisition															488.2
Total acquisition consideration (cash and non-cash)															$ 6,150.7
Business Acquisition, Share Price															$ 75.76
Noncash or Part Noncash Acquisition, Noncash Financial or Equity Instrument Consideration, Rate				26.86%
Acquisition Financing															$ 3,900,000.0
Business Acquisition, Transaction Costs	$ 6.9				166.0					6.9	166.0
Purchase Price Allocation [Abstract]
Net Proceeds from Debt																$ 2,870.2
Noncontrolling Interest Put [Abstract]
Proforma consolidated net revenue											$ 9,033.3
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax, Per Share, Basic											$ 1,117,200,000
Proforma consolidated net income											$ 547.5
Business Acquisition, Pro Forma Earnings Per Share, Basic											$ 5,050,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents															780.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables															334.8
Business Combination, Contingent Consideration, Asset, Current															138.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory															51.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets															261.4
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets															34.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment															844.2
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net															(3,176.1)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets															(15.2)
Business Combination, Separately Recognized Transactions, Assets Recognized															7,849.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable															190.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities															280.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue															168.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities, Current															730.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt															250.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other															78.5
Business Combination, Separately Recognized Transactions, Liabilities Recognized															1,698.3
Proforma consolidated diluted earnings per share											$ 5,030,000
Selling, General and Administrative Expenses [Member]
Business Acquisition [Line Items]
Other Special Charges										$ 9.0	$ 25.6
Selling, General and Administrative Expenses [Member] | Covance [Member]
Business Acquisition [Line Items]
Business Acquisition, Transaction Costs					113.4						113.4
Interest Expense [Member] | Covance [Member]
Business Acquisition [Line Items]
Business Acquisition, Transaction Costs					52.6						$ 52.6
60-Day Debt Bridge Traunche [Domain]
Cost of Acquired Entity [Abstract]
Bridge Term Credit Facility Agreement, Maximum Borrowing Amount																	$ 400.0
Short-term Debt, Terms											P60D
Software and Software Development Costs [Member] | Covance [Member]
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										10 years
Use Rights [Member]
Cost of Acquired Entity [Abstract]
Finite-lived Intangible Assets Acquired										$ 4.5
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					(4.9)						$ (4.9)				0.0
Use Rights [Member] | Covance [Member]
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										8 years
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill															(4.9)
Technology-Based Intangible Assets [Member]
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					(74.5)						(74.5)				(74.5)
Technology-Based Intangible Assets [Member] | Covance [Member]
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill															0.0
Trademarks and Trade Names [Member]
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					(18.9)						(18.9)				(270.5)
Trademarks and Trade Names [Member] | Covance [Member]
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										15 years
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill															(289.4)
Trade Names [Member]
Cost of Acquired Entity [Abstract]
Finite-lived Intangible Assets Acquired										$ 9.6
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										13 years 7 months
Customer Relationships [Member]
Cost of Acquired Entity [Abstract]
Finite-lived Intangible Assets Acquired										$ 168.2
Acquired Finite-lived Intangible Assets, Useful Life										28 years
Purchase Price Allocation [Abstract]
Weighted-average useful lives of identifiable intangible assets										16 years 1 month
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					(86.9)						(86.9)				(1,830.3)
Customer Relationships [Member] | Covance [Member]
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill															(1,917.2)
Off-Market Favorable Lease [Member]
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					$ (5.5)						$ (5.5)				(5.5)
Off-Market Favorable Lease [Member] | Covance [Member]
Noncontrolling Interest Put [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill															$ 0.0
Senior notes due 2018 [Member]
Business Acquisition [Line Items]
Long-term debt, less current portion		$ 130.0