BASIS OF FINANCIAL STATEMENT PRESENTATION	6 Months Ended
BASIS OF FINANCIAL STATEMENT PRESENTATION	Jun. 30, 2017
Accounting Policies [Abstract]
Basis of Financial Statement Presentation	BASIS OF FINANCIAL STATEMENT PRESENTATION Laboratory Corporation of America^® Holdings together with its subsidiaries (the Company) is a leading global life sciences company that is deeply integrated in guiding patient care, providing comprehensive clinical laboratory and end-to-end drug development services. The Company’s mission is to improve health and improve lives by delivering world-class diagnostic solutions, bringing innovative medicines to patients faster and using technology to improve the delivery of care. The Company serves a broad range of customers, including managed care organizations (MCOs), biopharmaceutical companies, governmental agencies, physicians and other healthcare providers (e.g., physician assistants and nurse practitioners, generally referred to herein as physicians), hospitals and health systems, employers, patients and consumers, contract research organizations, food and nutritional companies and independent clinical laboratories. The Company believes that it generated more revenue from laboratory testing than any other company in the world in 2016. The Company reports its business in two segments, LabCorp Diagnostics (LCD) and Covance Drug Development (CDD). For further financial information about these segments, see Note 14 (Business Segment Information). During the three months ended June 30, 2017, LCD and CDD contributed 72.0% and 28.0%, respectively, of net revenues to the Company. During the six months ended June 30, 2017, LCD and CDD contributed 71.7% and 28.3%, respectively, of net revenues to the Company. The condensed consolidated financial statements include the accounts of the Company and its majority-owned subsidiaries for which it exercises control. Long-term investments in affiliated companies in which the Company exercises significant influence, but which it does not control, are accounted for using the equity method. Investments in which the Company does not exercise significant influence (generally, when the Company has an investment of less than 20.0% and no representation on the investee's board of directors) are accounted for using the cost method. All significant inter-company transactions and accounts have been eliminated. The Company does not have any variable interest entities or special purpose entities whose financial results are not included in the condensed consolidated financial statements. The financial statements of the Company's operating foreign subsidiaries are measured using the local currency as the functional currency. Assets and liabilities are translated at exchange rates as of the balance sheet date. Revenues and expenses are translated at average monthly exchange rates prevailing during the period. Resulting translation adjustments are included in “Accumulated other comprehensive income.” The accompanying condensed consolidated financial statements of the Company are unaudited. In the opinion of management, all adjustments necessary for a fair statement of results of operations, cash flows and financial position have been made. Except as otherwise disclosed, all such adjustments are of a normal recurring nature. Interim results are not necessarily indicative of results for a full year. The year-end condensed consolidated balance sheet data was derived from audited financial statements but does not include all disclosures required by generally accepted accounting principles. The condensed consolidated financial statements and notes are presented in accordance with the rules and regulations of the Securities and Exchange Commission and do not contain certain information included in the Company’s 2016 Annual Report on Form 10-K. Therefore, the interim statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report. New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued the converged standard on revenue recognition with the objective of providing a single, comprehensive model for all contracts with customers to improve comparability in the financial statements of companies reporting using International Financial Reporting Standards and U.S. Generally Accepted Accounting Principles (GAAP). The standard contains principles that an entity must apply to determine the measurement of revenue and timing of when it is recognized. The underlying principle is that an entity must recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. An entity can apply the revenue standard retrospectively to each prior reporting period presented (full retrospective method) or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial application in retained earnings. The standard will be effective for the Company beginning January 1, 2018. The Company plans to adopt the full retrospective method effective January 1, 2018, and is continuing to evaluate the expected impact of the standard. Currently, the Company has completed the initial adoption analysis for LCD and expects this standard to impact LCD margins due to the recording of LCD bad debt expense against net revenues (versus selling, general and administrative expense) as an implicit price concession. The Company has also completed the initial adoption analysis for each of the major revenue streams within CDD and expects this standard to also impact CDD reported revenue and margins due to the inclusion of reimbursable out-of-pocket expenses in net revenues and net cost of sales, as well as the recognition of fees paid to investigators in net revenues and net costs of sales. In addition, the Company expects the timing of revenue recognition in the clinical business to accelerate, as revenue from study-related change orders and fixed price gains is recognized as the performance obligation is satisfied over the service period (versus the Company's current practice of lump-sum recognition resulting from a signed change order or when studies are near completion). The Company is currently performing a detailed contract review which must be completed before it can quantify the expected impact of the standard. The Company also anticipates enhanced financial statement disclosures surrounding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. In January 2016, the FASB issued a new accounting standard that addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. A financial instrument is defined as cash, evidence of ownership interest in a company or other entity, or a contract that both: (i) imposes on one entity a contractual obligation either to deliver cash or another financial instrument to a second entity or to exchange other financial instruments on potentially unfavorable terms with the second entity, and (ii) conveys to that second entity a contractual right either to receive cash or another financial instrument from the first entity or to exchange other financial instruments on potentially favorable terms with the first entity. The standard will be effective for the Company beginning January 1, 2018, with early adoption permitted. The Company is evaluating the impact that this new standard will have on the consolidated financial statements. In February 2016, the FASB issued a new accounting standard that sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for based on guidance similar to current guidance for operating leases. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. The standard is effective on January 1, 2019, with early adoption permitted. The Company has selected its leasing software solution and is evaluating the impact that this new standard will have on the consolidated financial statements. In June 2016, the FASB issued a new accounting standard intended to provide financial statement users with more decision-useful information about expected credit losses and other commitments to extend credit held by the reporting entity. The standard replaces the incurred loss impairment methodology in current GAAP with one that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The update is effective on January 1, 2020, with early adoption permitted. The Company is currently evaluating the impact this new standard will have on the consolidated financial statements. In August 2016, the FASB issued a new accounting standard that will make eight targeted changes to how cash receipts and cash payments are presented and classified in the statement of cash flows. This update is effective on January 1, 2018, and will require adoption on a retrospective basis. The Company expects the adoption of this standard to reclassify interest paid on its zero-coupon subordinated notes from a financing activity to an operating activity and potentially to impact the classification of deferred acquisition payments depending upon timing and amount of final payout. In January 2017, the FASB issued a new accounting standard that changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. This update is effective on January 1, 2018, with early adoption permitted. This adoption of this standard is not expected to have a material impact on the consolidated financial statements. In January 2017, the FASB issued a new accounting standard that eliminates Step 2 of the goodwill impairment test. Instead, an entity should perform its annual or interim goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. The update is effective for public business entities for the first interim and annual reporting periods beginning after January 1, 2020 with early adoption permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company has adopted this standard effective January 1, 2017, and will utilize this approach for any interim or annual goodwill impairment tests performed in 2017. In March 2017, the FASB issued a new accounting standard that requires employers that present a measure of operating income in their statement of income to include only the service cost component of net periodic pension cost and net periodic post-retirement benefit cost in operating expenses with other employee compensation costs. The other components of net benefit cost, including amortization of prior service cost/credit, and settlement and curtailment effects are to be included in non-operating expenses. This update is effective on January 1, 2018, with early adoption permitted. The Company is currently evaluating the impact this new standard will have on the consolidated financial statements. In May 2017, the FASB issued a new accounting standard that amends the scope of modification accounting for share-based payment arrangements and provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions, and classification of the awards are the same immediately before and after the modification. This update is effective on January 1, 2018, with early adoption permitted and should be applied prospectively to an award modified on or after the adoption date. The Company is currently evaluating the impact this new standard will have on the consolidated financial statements. Reclassifications The Company changed its financial statement classification for certain gross receipts taxes in 2016, removing these taxes from its provision for income taxes and moving this expense into selling, general and administrative expenses. Certain gross receipts taxes of $1.4 and $3.8 were reclassified in the three and six months ended June 30, 2016, respectively. In March 2016, the FASB issued a new accounting standard intended to simplify aspects of share-based payment accounting. The standard changes how companies account for certain aspects of share-based payment awards to employees, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as the classification of related matters in the statement of cash flows. The Company early adopted this standard in the quarter ended September 30, 2016. As a result of the adoption, a tax benefit of $5.9 and $9.8 was recorded for the three and six months ended June 30, 2016, respectively. Weighted average diluted shares for the three and six months ended June 30, 2016 increased by 0.2 and 0.2 due to the adoption of this standard.
Basis of Presentation and Significant Accounting Policies [Text Block]	BASIS OF FINANCIAL STATEMENT PRESENTATION Laboratory Corporation of America^® Holdings together with its subsidiaries (the Company) is a leading global life sciences company that is deeply integrated in guiding patient care, providing comprehensive clinical laboratory and end-to-end drug development services. The Company’s mission is to improve health and improve lives by delivering world-class diagnostic solutions, bringing innovative medicines to patients faster and using technology to improve the delivery of care. The Company serves a broad range of customers, including managed care organizations (MCOs), biopharmaceutical companies, governmental agencies, physicians and other healthcare providers (e.g., physician assistants and nurse practitioners, generally referred to herein as physicians), hospitals and health systems, employers, patients and consumers, contract research organizations, food and nutritional companies and independent clinical laboratories. The Company believes that it generated more revenue from laboratory testing than any other company in the world in 2016. The Company reports its business in two segments, LabCorp Diagnostics (LCD) and Covance Drug Development (CDD). For further financial information about these segments, see Note 14 (Business Segment Information). During the three months ended June 30, 2017, LCD and CDD contributed 72.0% and 28.0%, respectively, of net revenues to the Company. During the six months ended June 30, 2017, LCD and CDD contributed 71.7% and 28.3%, respectively, of net revenues to the Company. The condensed consolidated financial statements include the accounts of the Company and its majority-owned subsidiaries for which it exercises control. Long-term investments in affiliated companies in which the Company exercises significant influence, but which it does not control, are accounted for using the equity method. Investments in which the Company does not exercise significant influence (generally, when the Company has an investment of less than 20.0% and no representation on the investee's board of directors) are accounted for using the cost method. All significant inter-company transactions and accounts have been eliminated. The Company does not have any variable interest entities or special purpose entities whose financial results are not included in the condensed consolidated financial statements. The financial statements of the Company's operating foreign subsidiaries are measured using the local currency as the functional currency. Assets and liabilities are translated at exchange rates as of the balance sheet date. Revenues and expenses are translated at average monthly exchange rates prevailing during the period. Resulting translation adjustments are included in “Accumulated other comprehensive income.” The accompanying condensed consolidated financial statements of the Company are unaudited. In the opinion of management, all adjustments necessary for a fair statement of results of operations, cash flows and financial position have been made. Except as otherwise disclosed, all such adjustments are of a normal recurring nature. Interim results are not necessarily indicative of results for a full year. The year-end condensed consolidated balance sheet data was derived from audited financial statements but does not include all disclosures required by generally accepted accounting principles. The condensed consolidated financial statements and notes are presented in accordance with the rules and regulations of the Securities and Exchange Commission and do not contain certain information included in the Company’s 2016 Annual Report on Form 10-K. Therefore, the interim statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report. New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued the converged standard on revenue recognition with the objective of providing a single, comprehensive model for all contracts with customers to improve comparability in the financial statements of companies reporting using International Financial Reporting Standards and U.S. Generally Accepted Accounting Principles (GAAP). The standard contains principles that an entity must apply to determine the measurement of revenue and timing of when it is recognized. The underlying principle is that an entity must recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. An entity can apply the revenue standard retrospectively to each prior reporting period presented (full retrospective method) or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial application in retained earnings. The standard will be effective for the Company beginning January 1, 2018. The Company plans to adopt the full retrospective method effective January 1, 2018, and is continuing to evaluate the expected impact of the standard. Currently, the Company has completed the initial adoption analysis for LCD and expects this standard to impact LCD margins due to the recording of LCD bad debt expense against net revenues (versus selling, general and administrative expense) as an implicit price concession. The Company has also completed the initial adoption analysis for each of the major revenue streams within CDD and expects this standard to also impact CDD reported revenue and margins due to the inclusion of reimbursable out-of-pocket expenses in net revenues and net cost of sales, as well as the recognition of fees paid to investigators in net revenues and net costs of sales. In addition, the Company expects the timing of revenue recognition in the clinical business to accelerate, as revenue from study-related change orders and fixed price gains is recognized as the performance obligation is satisfied over the service period (versus the Company's current practice of lump-sum recognition resulting from a signed change order or when studies are near completion). The Company is currently performing a detailed contract review which must be completed before it can quantify the expected impact of the standard. The Company also anticipates enhanced financial statement disclosures surrounding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. In January 2016, the FASB issued a new accounting standard that addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. A financial instrument is defined as cash, evidence of ownership interest in a company or other entity, or a contract that both: (i) imposes on one entity a contractual obligation either to deliver cash or another financial instrument to a second entity or to exchange other financial instruments on potentially unfavorable terms with the second entity, and (ii) conveys to that second entity a contractual right either to receive cash or another financial instrument from the first entity or to exchange other financial instruments on potentially favorable terms with the first entity. The standard will be effective for the Company beginning January 1, 2018, with early adoption permitted. The Company is evaluating the impact that this new standard will have on the consolidated financial statements. In February 2016, the FASB issued a new accounting standard that sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for based on guidance similar to current guidance for operating leases. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. The standard is effective on January 1, 2019, with early adoption permitted. The Company has selected its leasing software solution and is evaluating the impact that this new standard will have on the consolidated financial statements. In June 2016, the FASB issued a new accounting standard intended to provide financial statement users with more decision-useful information about expected credit losses and other commitments to extend credit held by the reporting entity. The standard replaces the incurred loss impairment methodology in current GAAP with one that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The update is effective on January 1, 2020, with early adoption permitted. The Company is currently evaluating the impact this new standard will have on the consolidated financial statements. In August 2016, the FASB issued a new accounting standard that will make eight targeted changes to how cash receipts and cash payments are presented and classified in the statement of cash flows. This update is effective on January 1, 2018, and will require adoption on a retrospective basis. The Company expects the adoption of this standard to reclassify interest paid on its zero-coupon subordinated notes from a financing activity to an operating activity and potentially to impact the classification of deferred acquisition payments depending upon timing and amount of final payout. In January 2017, the FASB issued a new accounting standard that changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. This update is effective on January 1, 2018, with early adoption permitted. This adoption of this standard is not expected to have a material impact on the consolidated financial statements. In January 2017, the FASB issued a new accounting standard that eliminates Step 2 of the goodwill impairment test. Instead, an entity should perform its annual or interim goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. The update is effective for public business entities for the first interim and annual reporting periods beginning after January 1, 2020 with early adoption permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company has adopted this standard effective January 1, 2017, and will utilize this approach for any interim or annual goodwill impairment tests performed in 2017. In March 2017, the FASB issued a new accounting standard that requires employers that present a measure of operating income in their statement of income to include only the service cost component of net periodic pension cost and net periodic post-retirement benefit cost in operating expenses with other employee compensation costs. The other components of net benefit cost, including amortization of prior service cost/credit, and settlement and curtailment effects are to be included in non-operating expenses. This update is effective on January 1, 2018, with early adoption permitted. The Company is currently evaluating the impact this new standard will have on the consolidated financial statements. In May 2017, the FASB issued a new accounting standard that amends the scope of modification accounting for share-based payment arrangements and provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions, and classification of the awards are the same immediately before and after the modification. This update is effective on January 1, 2018, with early adoption permitted and should be applied prospectively to an award modified on or after the adoption date. The Company is currently evaluating the impact this new standard will have on the consolidated financial statements. Reclassifications The Company changed its financial statement classification for certain gross receipts taxes in 2016, removing these taxes from its provision for income taxes and moving this expense into selling, general and administrative expenses. Certain gross receipts taxes of $1.4 and $3.8 were reclassified in the three and six months ended June 30, 2016, respectively. In March 2016, the FASB issued a new accounting standard intended to simplify aspects of share-based payment accounting. The standard changes how companies account for certain aspects of share-based payment awards to employees, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as the classification of related matters in the statement of cash flows. The Company early adopted this standard in the quarter ended September 30, 2016. As a result of the adoption, a tax benefit of $5.9 and $9.8 was recorded for the three and six months ended June 30, 2016, respectively. Weighted average diluted shares for the three and six months ended June 30, 2016 increased by 0.2 and 0.2 due to the adoption of this standard.