ACCOUNTING POLICIES	12 Months Ended
Dec. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	2. ACCOUNTING POLICIES Basis of Presentation The consolidated financial statements include the accounts of WESCO International and all of its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. At the beginning of the third quarter of 2020, in connection with the acquisition of Anixter, the Company identified new operating segments. These operating segments, which have been organized around three strategic business units, consist of Electrical & Electronic Solutions ("EES"), Communications & Security Solutions ("CSS") and Utility & Broadband Solutions ("UBS"). The Company's operating segments, which are equivalent to its reportable segments, are described further in Note 17, "Business Segments". The applicable comparative financial information reported in the Company's previously issued consolidated financial statements for the years ended December 31, 2019 and 2018 has been recast in this Annual Report on Form 10-K to conform to the basis of the new segments. Out-of-Period Adjustment In the fourth quarter of 2020, management determined that the Company’s inventories were overstated by $60.3 million because of a misstatement in inventory cost absorption accounting, which occurred over multiple periods and also impacted inventories acquired in business combinations during those periods. Accordingly, the Consolidated Balance Sheet at December 31, 2020 reflects a reduction to inventories of $60.3 million, an increase to goodwill of $33.9 million and a decrease to deferred income tax liabilities of $12.0 million. The resulting effect of the out-of-period adjustment on the Consolidated Statement of Income and Comprehensive Income for the year ended December 31, 2020 was a $18.9 million increase to cost of goods sold, which decreased net income for the year by $14.4 million. Management concluded that this misstatement is not material to the current period or the financial statements of any previously filed annual or interim periods. Reclassifications The Consolidated Balance Sheet as of December 31, 2019, the Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2019 and 2018, and the Consolidated Statements of Cash Flows for the years ended December 31, 2019 and 2018, respectively, include certain reclassifications to previously reported amounts to conform to the current period's presentation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates are based on management’s best knowledge of current events and actions WESCO may undertake in the future, actual results may ultimately differ from the estimates. Revenue Recognition WESCO’s revenue arrangements generally consist of single performance obligations to transfer a promised good or service, or a combination of goods and services. Revenue is measured as the amount of consideration WESCO expects to receive in exchange for transferring goods or providing services. Revenue is recognized when control has transferred to the customer, which is generally when the product has shipped from a WESCO facility or directly from a supplier. However, transfer may occur at a later date depending on the agreed upon terms, such as delivery at the customer's designated location, or based on consignment terms. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. When providing services, sales are recognized over time as control transfers to the customer, which occurs as services are rendered. WESCO generally satisfies its performance obligations within a year or less. WESCO generally does not have significant financing terms associated with its contracts; payments are normally received within 60 days. There are generally no significant costs associated with obtaining customer contracts. WESCO typically passes through warranties offered by manufacturers or suppliers to its customers. Sales taxes (and value added taxes in foreign jurisdictions) collected from customers and remitted to governmental authorities are excluded from net sales. Supplier Volume Rebates WESCO receives volume rebates from certain suppliers based on contractual arrangements with such suppliers. Volume rebates are included within other accounts receivable in the Consolidated Balance Sheets, and represent the estimated amounts due to WESCO based on forecasted purchases and the rebate provisions of the various supplier contracts. The corresponding rebate income is recorded as a reduction to cost of goods sold. Receivables under the supplier rebate program were $136.7 million at December 31, 2020 and $81.6 million at December 31, 2019. The supplier volume rebate income as a percentage of net sales was 1.1% in 2020, 1.2% in 2019 and 1.3% in 2018. Cash Equivalents Cash equivalents are defined as highly liquid investments with original maturities of 90 days or less when purchased. Allowance for Expected Credit Losses WESCO recognizes expected credit losses resulting from the inability of its customers to make required payments through an allowance account that is measured each reporting date. WESCO estimates credit losses over the life of its trade accounts receivable using a combination of historical loss data, current credit conditions, specific customer circumstances, and reasonable and supportable forecasts of future economic conditions. The allowance for expected credit losses was $23.9 million at December 31, 2020 and $25.4 million at December 31, 2019. The total amount recorded as selling, general and administrative expense related to credit losses was $10.1 million, $7.0 million and $10.9 million for 2020, 2019 and 2018, respectively. Inventories Inventories primarily consist of merchandise purchased for resale and are stated at the lower of cost and net realizable value. Cost is determined principally under the average cost method. WESCO reduces the carrying value of its inventories at the earlier of identifying an item that is considered to be obsolete or in excess of supply relative to demand, or no movement in the past 15 months. Reserves for excess and obsolete inventories were $28.7 million and $30.7 million at December 31, 2020 and 2019, respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $15.7 million, $10.0 million and $9.7 million for 2020, 2019 and 2018, respectively. Property, Buildings and Equipment Property, buildings and equipment are recorded at cost. Depreciation expense is determined using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over either their respective lease terms or their estimated lives, whichever is shorter. Estimated useful lives range from five to forty years for buildings and leasehold improvements and two to ten years for furniture, fixtures and equipment. Costs incurred during the application development stage of internally developing software are capitalized and are reported at the lower of unamortized cost or net realizable value. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Capitalized costs include external direct costs of materials and services consumed in developing internal-use computer software, payroll and payroll-related costs for employees who are directly associated with and who devote time to the internal-use computer software project and interest costs. Internal-use computer software is amortized using the straight-line method over its estimated useful life, typically three to seven years. Expenditures for new facilities and improvements that extend the useful life of an asset are capitalized. Ordinary repairs and maintenance are expensed as incurred. When property is retired or otherwise disposed of, the cost and the related accumulated depreciation are removed from the accounts and any resulting gains or losses are recorded and reported as selling, general and administrative expenses. Of WESCO’s $399.2 million net book value of property, buildings and equipment as of December 31, 2020, $144.1 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 800 branches, warehouses and sales offices, mitigating the risk of impairment. WESCO assesses its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of any such assets may not be fully recoverable. Changes in circumstances include technological advances, changes in the business model, capital structure, economic conditions or operating performance. The evaluation is based upon, among other things, utilization, serviceability and assumptions developed by management, which are categorized as Level 3 of the fair value hierarchy, related to the estimated future undiscounted cash flows that these assets are expected to generate. When the sum of the undiscounted cash flows is less than the carrying value of the asset or asset group, an impairment loss is recognized to the extent that carrying value exceeds fair value. Management applies its best judgment when performing these evaluations. Leases The determination of whether an arrangement is, or contains, a lease is performed at the inception of the arrangement. Classification and initial measurement of the right-of-use asset and lease liability are determined at the lease commencement date. The Company elected the short-term lease measurement and recognition exemption; therefore, leases with an initial term of 12 months or less are not recorded on the balance sheet. Operating lease expense is recognized on a straight-line basis over the lease term. Operating lease assets and liabilities are recognized at the commencement date based on the present value of the future minimum lease payments. Certain leases contain rent escalation clauses that are either fixed or adjusted periodically for inflation or market rates and such clauses are factored into the Company's determination of lease payments. WESCO also has variable lease payments that do not depend on a rate or index, primarily for items such as common area maintenance and real estate taxes, which are recorded as variable expense when incurred. The operating lease asset includes advance payments and excludes incentives and initial direct costs incurred. The Company's arrangements include certain non-lease components such as common area and other maintenance for leased real estate, as well as mileage, fuel and maintenance costs related to leased automobiles and trucks. WESCO accounts for these nonlease components separately from the associated lease components. The Company does not guarantee any residual value in its lease agreements, and there are no material restrictions or covenants imposed by lease arrangements. Real estate leases typically include one or more options to extend the lease, or terminate early. The Company regularly evaluates the renewal options, and when they are reasonably certain of exercise, the Company includes the renewal period in its lease term. For most of WESCO’s leases, the discount rate implicit in the lease is not readily determinable. Accordingly, the Company uses its incremental borrowing rate based on the information available at the lease commencement date to discount lease payments to the present value. Goodwill and Indefinite-Lived Intangible Assets Goodwill and indefinite-lived intangible assets are tested for impairment annually during the fourth quarter using information available at the end of September, or more frequently if triggering events occur, indicating that their carrying value may not be recoverable. WESCO tests for goodwill impairment on a reporting unit level. The Company first assesses qualitative factors, including macroeconomic conditions, industry and market considerations, cost factors, overall financial performance, other relevant events such as changes in key personnel, changes in the composition or carrying amount of the net assets of a reporting unit, and sustained decreases in share price, to determine whether it is more likely than not that the fair value of WESCO's reporting units are less than their carrying values. If the qualitative assessment indicates that the fair values of the Company's reporting units may not exceed their respective carrying values, then WESCO performs a quantitative test for impairment by comparing the fair value of each reporting unit to its carrying value. The Company determines the fair values of its reporting units using a discounted cash flow analysis and consideration of market multiples. The discounted cash flow analysis uses certain assumptions, including expected operating margins supported by a combination of historical results, current forecasts, market data and recent economic events, which are categorized within Level 3 of the fair value hierarchy. The Company uses a discount rate that reflects market participants' cost of capital. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2020 and 2019, goodwill and indefinite-lived trademarks totaled $4.0 billion and $1.9 billion, respectively. The determination of fair value involves significant management judgment, particularly as it relates to the underlying assumptions and factors around expected operating margins and discount rate. Management applies its best judgment when assessing the reasonableness of financial projections. Fair values are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill and indefinite-lived intangible impairment tests will prove to be an accurate prediction of future results. Definite Lived Intangible Assets Definite lived intangible assets are amortized over 2 to 20 years. Certain customer relationships are amortized using an accelerated method whereas all other definite lived intangible assets subject to amortization use a straight-line method. In either case, the amortization method reflects the pattern in which the economic benefits of the respective assets are consumed or otherwise used. WESCO continually evaluates whether events or circumstances have occurred that would indicate the remaining estimated useful lives of definite lived intangible assets require revision or that the remaining carrying value of such assets may not be recoverable. Insurance Programs WESCO uses commercial insurance for auto, workers’ compensation, casualty and health claims, and information technology as a risk-reduction strategy to minimize catastrophic losses. The Company’s strategy involves large deductible policies where WESCO must pay all costs up to the deductible amount. WESCO estimates the reserve for these programs based on historical incident rates and costs. The assumptions included in developing this accrual include the period of time between the incurrence and payment of a claim. The total liability related to insurance programs was $27.9 million and $12.9 million at December 31, 2020 and 2019, respectively. Income Taxes WESCO accounts for income taxes under the asset and liability method, which requires the recognition of deferred income taxes for events that have future tax consequences. Under this method, deferred income taxes are recognized (using enacted tax laws and rates) based on the future income tax effects of differences in the carrying amounts of assets and liabilities for financial reporting and tax purposes. The effect of a tax rate change on deferred tax assets and liabilities is recognized in income in the period of change. WESCO recognizes deferred tax assets at amounts that are expected to be realized. To make such determination, management evaluates all positive and negative evidence, including but not limited to, prior, current and future taxable income, tax planning strategies and future reversals of existing taxable temporary differences. A valuation allowance is recognized if it is “more-likely-than-not” that some or all of a deferred tax asset will not be realized. WESCO regularly assesses the realizability of deferred tax assets. WESCO accounts for uncertainty in income taxes using a "more-likely-than-not" recognition threshold. Due to the subjectivity inherent in the evaluation of uncertain tax positions, the tax benefit ultimately recognized may materially differ from the estimate recognized in the consolidated financial statements. WESCO recognizes interest and penalties related to uncertain tax benefits as part of interest expense and income tax expense, respectively. The Tax Cuts and Jobs Act of 2017 (the “TCJA”) imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the “transition tax”). Except for a portion of foreign earnings previously taxed in the U.S. that can effectively be distributed without further material U.S. or foreign taxation, the Company continues to assert that the undistributed earnings of its foreign subsidiaries are indefinitely reinvested. To the extent the earnings of the Company's foreign subsidiaries are distributed in the form of dividends, such earnings may be subject to additional taxes. The Company believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without incurring any material tax cost to repatriate cash held by its foreign subsidiaries. The provisions of the TCJA also introduced U.S. taxation on certain global intangible low-taxed income ("GILTI"). WESCO has elected to account for GILTI tax as a component of income tax expense. Foreign Currency The local currency is the functional currency for most of the Company's operations outside the U.S. Assets and liabilities of these operations are translated to U.S. dollars at the exchange rate in effect at the end of each period. Income statement accounts are translated at an exchange rate that approximates the average for the period. Translation adjustments arising from the use of differing exchange rates from period to period are included as a component of other comprehensive income (loss) within stockholders’ equity. Gains and losses from foreign currency transactions are included in net income for the period. Defined Benefit Pension Plan Liabilities and expenses for pension benefits are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated cash flows, the expected long-term rate of return on plan assets, and several assumptions relating to the employee workforce (salary increases, retirement age, and mortality). Unrealized gains and losses related to the Company's defined benefit pension obligations are recognized as a component of other comprehensive income (loss) within stockholders' equity. Fair Value of Financial Instruments The Company measures the fair value of assets and liabilities on a recurring and nonrecurring basis according to a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value and requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible at the measurement date; Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, and Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to measurements involving significant unobservable inputs (Level 3). The Company measures the fair values of goodwill, intangible assets and property, buildings and equipment on a nonrecurring basis if required by impairment tests applicable to these assets, as described above. Other, net Other non-operating income and expenses ("other, net") primarily includes the non-service cost components of net periodic pension cost (benefit) and foreign exchange gains and losses. Recently Adopted Accounting Pronouncements Effective January 1, 2019, WESCO adopted Accounting Standards Update (ASU) 2016-02, Leases, and all the related amendments (“Topic 842”), a comprehensive new standard that amended various aspects of existing accounting guidance for leases. The adoption of Topic 842 resulted in the recognition of right-of-use assets and lease liabilities for operating leases of approximately $240 million and $245 million, respectively, in the Consolidated Balance Sheet as of January 1, 2019, most of which relate to real estate. The adoption of Topic 842 did not have a material impact on the Consolidated Statements of Income and Comprehensive Income or Consolidated Statements of Cash Flows for the year ended December 31, 2019. The Company used the optional effective date transition method and therefore did not adjust the prior comparative periods presented herein. There was no cumulative-effect adjustment to beginning retained earnings as a result of using this method. In addition, the Company elected the package of practical expedients that allowed the adoption of Topic 842 without reassessing arrangements that commenced prior to the effective date. Additional qualitative and quantitative information about the Company's leases is disclosed in Note 9, "Leases". In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which introduced new guidance for the accounting for credit losses on certain financial instruments. The Company adopted this ASU effective January 1, 2020. The adoption of this new credit loss guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein, and WESCO does not expect it to have a material impact on its financial position or results of operation on an ongoing basis. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which amends the disclosure requirements for recurring and nonrecurring fair value measurements by removing, modifying and adding certain disclosures. The Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which aligned the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The standard was effective for fiscal years beginning after December 15, 2019. The Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, which amends the disclosure requirements for all employers that sponsor defined benefit pension and other post retirement plans by removing and adding certain disclosures. The amendments in this ASU are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. The Company adopted this ASU in the fourth quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. Recently Issued Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which removes certain exceptions to the general principles of Accounting Standards Codification Topic 740, Income Taxes, and simplifies other aspects of accounting for income taxes. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted in any interim or annual period, with any adjustments reflected as of the beginning of the fiscal year of adoption. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in this Update are effective for all entities as of March 12, 2020 through December 31, 2022. Management is currently evaluating the impact related to the replacement of London Interbank Offered Rate (LIBOR) and whether the Company will elect the adoption of the optional guidance. Other pronouncements issued by the FASB or other authoritative accounting standards groups with future effective dates are either not applicable or are not expected to be significant to WESCO’s financial position, results of operations or cash flows.

At the beginning of the third quarter of 2020, in connection with the acquisition of Anixter, the Company identified new operating segments. These operating segments, which have been organized around three strategic business units, consist of Electrical & Electronic Solutions ("EES"), Communications & Security Solutions ("CSS") and Utility & Broadband Solutions ("UBS"). The Company's operating segments, which are equivalent to its reportable segments, are described further in Note 17, "Business Segments". The applicable comparative financial information reported in the Company's previously issued consolidated financial statements for the years ended December 31, 2019 and 2018 has been recast in this Annual Report on Form 10-K to conform to the basis of the new segments.

In the fourth quarter of 2020, management determined that the Company’s inventories were overstated by $60.3 million because of a misstatement in inventory cost absorption accounting, which occurred over multiple periods and also impacted inventories acquired in business combinations during those periods. Accordingly, the Consolidated Balance Sheet at December 31, 2020 reflects a reduction to inventories of $60.3 million, an increase to goodwill of $33.9 million and a decrease to deferred income tax liabilities of $12.0 million. The resulting effect of the out-of-period adjustment on the Consolidated Statement of Income and Comprehensive Income for the year ended December 31, 2020 was a $18.9 million increase to cost of goods sold, which decreased net income for the year by $14.4 million. Management concluded that this misstatement is not material to the current period or the financial statements of any previously filed annual or interim periods.

The Consolidated Balance Sheet as of December 31, 2019, the Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2019 and 2018, and the Consolidated Statements of Cash Flows for the years ended December 31, 2019 and 2018, respectively, include certain reclassifications to previously reported amounts to conform to the current period's presentation.

The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates are based on management’s best knowledge of current events and actions WESCO may undertake in the future, actual results may ultimately differ from the estimates.

WESCO’s revenue arrangements generally consist of single performance obligations to transfer a promised good or service, or a combination of goods and services. Revenue is measured as the amount of consideration WESCO expects to receive in exchange for transferring goods or providing services. Revenue is recognized when control has transferred to the customer, which is generally when the product has shipped from a WESCO facility or directly from a supplier. However, transfer may occur at a later date depending on the agreed upon terms, such as delivery at the customer's designated location, or based on consignment terms. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. When providing services, sales are recognized over time as control transfers to the customer, which occurs as services are rendered. WESCO generally satisfies its performance obligations within a year or less.

WESCO generally does not have significant financing terms associated with its contracts; payments are normally received within 60 days. There are generally no significant costs associated with obtaining customer contracts. WESCO typically passes through warranties offered by manufacturers or suppliers to its customers. Sales taxes (and value added taxes in foreign jurisdictions) collected from customers and remitted to governmental authorities are excluded from net sales.

WESCO receives volume rebates from certain suppliers based on contractual arrangements with such suppliers. Volume rebates are included within other accounts receivable in the Consolidated Balance Sheets, and represent the estimated amounts due to WESCO based on forecasted purchases and the rebate provisions of the various supplier contracts. The corresponding rebate income is recorded as a reduction to cost of goods sold. Receivables under the supplier rebate program were $136.7 million at December 31, 2020 and $81.6 million at December 31, 2019. The supplier volume rebate income as a percentage of net sales was 1.1% in 2020, 1.2% in 2019 and 1.3% in 2018.

WESCO recognizes expected credit losses resulting from the inability of its customers to make required payments through an allowance account that is measured each reporting date. WESCO estimates credit losses over the life of its trade accounts receivable using a combination of historical loss data, current credit conditions, specific customer circumstances, and reasonable and supportable forecasts of future economic conditions. The allowance for expected credit losses was $23.9 million at December 31, 2020 and $25.4 million at December 31, 2019. The total amount recorded as selling, general and administrative expense related to credit losses was $10.1 million, $7.0 million and $10.9 million for 2020, 2019 and 2018, respectively.

Inventories primarily consist of merchandise purchased for resale and are stated at the lower of cost and net realizable value. Cost is determined principally under the average cost method. WESCO reduces the carrying value of its inventories at the earlier of identifying an item that is considered to be obsolete or in excess of supply relative to demand, or no movement in the past 15 months. Reserves for excess and obsolete inventories were $28.7 million and $30.7 million at December 31, 2020 and 2019, respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $15.7 million, $10.0 million and $9.7 million for 2020, 2019 and 2018, respectively.

Property, buildings and equipment are recorded at cost. Depreciation expense is determined using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over either their respective lease terms or their estimated lives, whichever is shorter. Estimated useful lives range from five to forty years for buildings and leasehold improvements and two to ten years for furniture, fixtures and equipment.

Costs incurred during the application development stage of internally developing software are capitalized and are reported at the lower of unamortized cost or net realizable value. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Capitalized costs include external direct costs of materials and services consumed in developing internal-use computer software, payroll and payroll-related costs for employees who are directly associated with and who devote time to the internal-use computer software project and interest costs. Internal-use computer software is amortized using the straight-line method over its estimated useful life, typically three to seven years.

Expenditures for new facilities and improvements that extend the useful life of an asset are capitalized. Ordinary repairs and maintenance are expensed as incurred. When property is retired or otherwise disposed of, the cost and the related accumulated depreciation are removed from the accounts and any resulting gains or losses are recorded and reported as selling, general and administrative expenses.

Of WESCO’s $399.2 million net book value of property, buildings and equipment as of December 31, 2020, $144.1 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 800 branches, warehouses and sales offices, mitigating the risk of impairment. WESCO assesses its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of any such assets may not be fully recoverable. Changes in circumstances include technological advances, changes in the business model, capital structure, economic conditions or operating performance. The evaluation is based upon, among other things, utilization, serviceability and assumptions developed by management, which are categorized as Level 3 of the fair value hierarchy, related to the estimated future undiscounted cash flows that these assets are expected to generate. When the sum of the undiscounted cash flows is less than the carrying value of the asset or asset group, an impairment loss is recognized to the extent that carrying value exceeds fair value. Management applies its best judgment when performing these evaluations.

The determination of whether an arrangement is, or contains, a lease is performed at the inception of the arrangement. Classification and initial measurement of the right-of-use asset and lease liability are determined at the lease commencement date. The Company elected the short-term lease measurement and recognition exemption; therefore, leases with an initial term of 12 months or less are not recorded on the balance sheet. Operating lease expense is recognized on a straight-line basis over the lease term.

Operating lease assets and liabilities are recognized at the commencement date based on the present value of the future minimum lease payments. Certain leases contain rent escalation clauses that are either fixed or adjusted periodically for inflation or market rates and such clauses are factored into the Company's determination of lease payments. WESCO also has variable lease payments that do not depend on a rate or index, primarily for items such as common area maintenance and real estate taxes, which are recorded as variable expense when incurred. The operating lease asset includes advance payments and excludes incentives and initial direct costs incurred.

The Company's arrangements include certain non-lease components such as common area and other maintenance for leased real estate, as well as mileage, fuel and maintenance costs related to leased automobiles and trucks. WESCO accounts for these nonlease components separately from the associated lease components. The Company does not guarantee any residual value in its lease agreements, and there are no material restrictions or covenants imposed by lease arrangements. Real estate leases typically include one or more options to extend the lease, or terminate early. The Company regularly evaluates the renewal options, and when they are reasonably certain of exercise, the Company includes the renewal period in its lease term. For most of WESCO’s leases, the discount rate implicit in the lease is not readily determinable. Accordingly, the Company uses its incremental borrowing rate based on the information available at the lease commencement date to discount lease payments to the present value.

Goodwill and indefinite-lived intangible assets are tested for impairment annually during the fourth quarter using information available at the end of September, or more frequently if triggering events occur, indicating that their carrying value may not be recoverable. WESCO tests for goodwill impairment on a reporting unit level. The Company first assesses qualitative factors, including macroeconomic conditions, industry and market considerations, cost factors, overall financial performance, other relevant events such as changes in key personnel, changes in the composition or carrying amount of the net assets of a reporting unit, and sustained decreases in share price, to determine whether it is more likely than not that the fair value of WESCO's reporting units are less than their carrying values. If the qualitative assessment indicates that the fair values of the Company's reporting units may not exceed their respective carrying values, then WESCO performs a quantitative test for impairment by comparing the fair value of each reporting unit to its carrying value. The Company determines the fair values of its reporting units using a discounted cash flow analysis and consideration of market multiples. The discounted cash flow analysis uses certain assumptions, including expected operating margins supported by a combination of historical results, current forecasts, market data and recent economic events, which are categorized within Level 3 of the fair value hierarchy. The Company uses a discount rate that reflects market participants' cost of capital. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2020 and 2019, goodwill and indefinite-lived trademarks totaled $4.0 billion and $1.9 billion, respectively.

The determination of fair value involves significant management judgment, particularly as it relates to the underlying assumptions and factors around expected operating margins and discount rate. Management applies its best judgment when assessing the reasonableness of financial projections. Fair values are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill and indefinite-lived intangible impairment tests will prove to be an accurate prediction of future results.

Definite lived intangible assets are amortized over 2 to 20 years. Certain customer relationships are amortized using an accelerated method whereas all other definite lived intangible assets subject to amortization use a straight-line method. In either case, the amortization method reflects the pattern in which the economic benefits of the respective assets are consumed or otherwise used. WESCO continually evaluates whether events or circumstances have occurred that would indicate the remaining estimated useful lives of definite lived intangible assets require revision or that the remaining carrying value of such assets may not be recoverable.

WESCO uses commercial insurance for auto, workers’ compensation, casualty and health claims, and information technology as a risk-reduction strategy to minimize catastrophic losses. The Company’s strategy involves large deductible policies where WESCO must pay all costs up to the deductible amount. WESCO estimates the reserve for these programs based on historical incident rates and costs. The assumptions included in developing this accrual include the period of time between the incurrence and payment of a claim. The total liability related to insurance programs was $27.9 million and $12.9 million at December 31, 2020 and 2019, respectively.

WESCO accounts for income taxes under the asset and liability method, which requires the recognition of deferred income taxes for events that have future tax consequences. Under this method, deferred income taxes are recognized (using enacted tax laws and rates) based on the future income tax effects of differences in the carrying amounts of assets and liabilities for financial reporting and tax purposes. The effect of a tax rate change on deferred tax assets and liabilities is recognized in income in the period of change.

WESCO recognizes deferred tax assets at amounts that are expected to be realized. To make such determination, management evaluates all positive and negative evidence, including but not limited to, prior, current and future taxable income, tax planning strategies and future reversals of existing taxable temporary differences. A valuation allowance is recognized if it is “more-likely-than-not” that some or all of a deferred tax asset will not be realized. WESCO regularly assesses the realizability of deferred tax assets.

WESCO accounts for uncertainty in income taxes using a "more-likely-than-not" recognition threshold. Due to the subjectivity inherent in the evaluation of uncertain tax positions, the tax benefit ultimately recognized may materially differ from the estimate recognized in the consolidated financial statements. WESCO recognizes interest and penalties related to uncertain tax benefits as part of interest expense and income tax expense, respectively.

The Tax Cuts and Jobs Act of 2017 (the “TCJA”) imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the “transition tax”). Except for a portion of foreign earnings previously taxed in the U.S. that can effectively be distributed without further material U.S. or foreign taxation, the Company continues to assert that the undistributed earnings of its foreign subsidiaries are indefinitely reinvested. To the extent the earnings of the Company's foreign subsidiaries are distributed in the form of dividends, such earnings may be subject to additional taxes. The Company believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without incurring any material tax cost to repatriate cash held by its foreign subsidiaries.

The local currency is the functional currency for most of the Company's operations outside the U.S. Assets and liabilities of these operations are translated to U.S. dollars at the exchange rate in effect at the end of each period. Income statement accounts are translated at an exchange rate that approximates the average for the period. Translation adjustments arising from the use of differing exchange rates from period to period are included as a component of other comprehensive income (loss) within stockholders’ equity. Gains and losses from foreign currency transactions are included in net income for the period.

Liabilities and expenses for pension benefits are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated cash flows, the expected long-term rate of return on plan assets, and several assumptions relating to the employee workforce (salary increases, retirement age, and mortality). Unrealized gains and losses related to the Company's defined benefit pension obligations are recognized as a component of other comprehensive income (loss) within stockholders' equity.

The Company measures the fair value of assets and liabilities on a recurring and nonrecurring basis according to a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value and requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible at the measurement date; Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, and Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to measurements involving significant unobservable inputs (Level 3).

Effective January 1, 2019, WESCO adopted Accounting Standards Update (ASU) 2016-02, Leases, and all the related amendments (“Topic 842”), a comprehensive new standard that amended various aspects of existing accounting guidance for leases. The adoption of Topic 842 resulted in the recognition of right-of-use assets and lease liabilities for operating leases of approximately $240 million and $245 million, respectively, in the Consolidated Balance Sheet as of January 1, 2019, most of which relate to real estate. The adoption of Topic 842 did not have a material impact on the Consolidated Statements of Income and Comprehensive Income or Consolidated Statements of Cash Flows for the year ended December 31, 2019.

The Company used the optional effective date transition method and therefore did not adjust the prior comparative periods presented herein. There was no cumulative-effect adjustment to beginning retained earnings as a result of using this method. In addition, the Company elected the package of practical expedients that allowed the adoption of Topic 842 without reassessing arrangements that commenced prior to the effective date. Additional qualitative and quantitative information about the Company's leases is disclosed in Note 9, "Leases".

In June 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which introduced new guidance for the accounting for credit losses on certain financial instruments. The Company adopted this ASU effective January 1, 2020. The adoption of this new credit loss guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein, and WESCO does not expect it to have a material impact on its financial position or results of operation on an ongoing basis.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which amends the disclosure requirements for recurring and nonrecurring fair value measurements by removing, modifying and adding certain disclosures. The Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein.

In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which aligned the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The standard was effective for fiscal years beginning after December 15, 2019. The Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein.

In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, which amends the disclosure requirements for all employers that sponsor defined benefit pension and other post retirement plans by removing and adding certain disclosures. The amendments in this ASU are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. The Company adopted this ASU in the fourth quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which removes certain exceptions to the general principles of Accounting Standards Codification Topic 740, Income Taxes, and simplifies other aspects of accounting for income taxes. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted in any interim or annual period, with any adjustments reflected as of the beginning of the fiscal year of adoption. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto.

In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in this Update are effective for all entities as of March 12, 2020 through December 31, 2022. Management is currently evaluating the impact related to the replacement of London Interbank Offered Rate (LIBOR) and whether the Company will elect the adoption of the optional guidance.