Business, Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) for interim financial information and with the instructions for Form 10-Q and Rule 10-01 of Regulation S-X. Pursuant to these rules and regulations, certain information and footnote disclosures normally included in the annual audited consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. The accompanying condensed consolidated balance sheet as of December 31, 2017 is derived from the Company’s audited financial statements as of that date. Because certain information and footnote disclosures have been condensed or omitted, these condensed unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto as of and for the year ended December 31, 2017 contained in the Company’s 2017 Annual Report on Form 10-K (the “2017 Form 10-K”). In management’s opinion, all normal and recurring adjustments considered necessary for a fair presentation of the financial position, results of operations and cash flows for the periods presented have been included. Certain prior year amounts have been reclassified to conform to the current period presentation. Interim period operating results do not necessarily indicate the results that may be expected for any other interim period or for the full fiscal year. The Company believes that the disclosures made in these condensed unaudited consolidated financial statements are adequate to make the information not misleading.
Reclassifications	Certain prior year amounts have been reclassified to conform to the current period presentation.
Principles of Consolidation	Principles of Consolidation The accompanying condensed unaudited consolidated financial statements include MasTec, Inc. and its subsidiaries and include the accounts of all majority owned subsidiaries over which the Company exercises control and, when applicable, entities in which the Company has a controlling financial interest. All significant intercompany balances and transactions have been eliminated in consolidation. Other parties’ interests in entities that MasTec consolidates are reported as non-controlling interests within equity. Net income or loss attributable to non-controlling interests is reported as a separate line item below net income or loss. The Company’s investments in entities for which the Company does not have a controlling interest, but for which it has the ability to exert significant influence, are accounted for using either the equity method of accounting or under the fair value option. Equity method investments are recorded as other long-term assets. Income or loss from these investments is recorded as a separate line item in the statements of operations. Intercompany profits or losses associated with the Company’s equity method investments are eliminated until realized by the investee in transactions with third parties. For equity investees in which the Company has an undivided interest in the assets, liabilities and profits or losses of an unincorporated entity, but the Company does not exercise control over the entity, the Company consolidates its proportional interest in the accounts of the entity. Equity investments, other than those accounted for as equity method investments or those that are consolidated, are measured at fair value if their fair values are readily determinable. Equity investments that do not have readily determinable fair values are measured at cost, adjusted for changes from observable market transactions, less impairment. Realized and unrealized gains or losses related to equity investments are recognized in other income or expense. Management determines whether each business entity in which it has equity interests, debt, or other investments constitutes a variable interest entity (“VIE”) based on the nature and characteristics of such arrangements. If an investment arrangement is determined to be a VIE, then management determines if the Company is the VIE’s primary beneficiary by evaluating several factors, including the Company’s: (i) risks and responsibilities; (ii) ownership interests; (iii) decision making powers; and (iv) financial interests, among other factors. If management determines the Company is the primary beneficiary of a VIE, then it would be consolidated, and other parties’ interests in the VIE would be accounted for as non-controlling interests. The primary beneficiary consolidating the VIE must normally have both (i) the power to direct the primary activities of the VIE and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE, which, in either case, could be significant to the VIE. As of September 30, 2018, the Company determined that certain of its investment arrangements were VIEs. The Company does not, however, have the power to direct the primary activities that most significantly impact the economic performance of these VIEs and the Company is not the primary beneficiary; accordingly, it has not consolidated these VIEs.
Equity Method Investments	The Company’s investments in entities for which the Company does not have a controlling interest, but for which it has the ability to exert significant influence, are accounted for using either the equity method of accounting or under the fair value option. Equity method investments are recorded as other long-term assets. Income or loss from these investments is recorded as a separate line item in the statements of operations. Intercompany profits or losses associated with the Company’s equity method investments are eliminated until realized by the investee in transactions with third parties.
Unincorporated Entities, Proportionate Consolidation	For equity investees in which the Company has an undivided interest in the assets, liabilities and profits or losses of an unincorporated entity, but the Company does not exercise control over the entity, the Company consolidates its proportional interest in the accounts of the entity.
Other Equity Investments With Readily Determinable Fair Values	Equity investments, other than those accounted for as equity method investments or those that are consolidated, are measured at fair value if their fair values are readily determinable.
Other Equity Investments Without Readily Determinable Fair Values	Equity investments that do not have readily determinable fair values are measured at cost, adjusted for changes from observable market transactions, less impairment. Realized and unrealized gains or losses related to equity investments are recognized in other income or expense.
Variable Interest Entities	Management determines whether each business entity in which it has equity interests, debt, or other investments constitutes a variable interest entity (“VIE”) based on the nature and characteristics of such arrangements. If an investment arrangement is determined to be a VIE, then management determines if the Company is the VIE’s primary beneficiary by evaluating several factors, including the Company’s: (i) risks and responsibilities; (ii) ownership interests; (iii) decision making powers; and (iv) financial interests, among other factors. If management determines the Company is the primary beneficiary of a VIE, then it would be consolidated, and other parties’ interests in the VIE would be accounted for as non-controlling interests. The primary beneficiary consolidating the VIE must normally have both (i) the power to direct the primary activities of the VIE and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE, which, in either case, could be significant to the VIE. As of September 30, 2018, the Company determined that certain of its investment arrangements were VIEs. The Company does not, however, have the power to direct the primary activities that most significantly impact the economic performance of these VIEs and the Company is not the primary beneficiary; accordingly, it has not consolidated these VIEs.
Translation of Foreign Currencies	Translation of Foreign Currencies The assets and liabilities of foreign subsidiaries with a functional currency other than the U.S. dollar are translated into U.S. dollars at period-end exchange rates, with resulting translation gains or losses accumulated within other comprehensive income or loss. Revenue and expenses are translated into U.S. dollars at average rates of exchange during the applicable period. Substantially all of the Company’s foreign operations use their local currency as their functional currency. Currency gains or losses resulting from transactions executed in currencies other than the functional currency are included in other income or expense, net.
Management Estimates	Management Estimates The preparation of consolidated financial statements in accordance with U.S. GAAP requires the use of estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. These estimates are based on historical experience and various other assumptions, the results of which form the basis of making judgments about the Company’s operating results and the carrying values of assets and liabilities that are not readily apparent from other sources. Key estimates include: the recognition of revenue and project profit or loss, which the Company defines as project revenue, less project costs of revenue, including project-related depreciation, in particular, on construction contracts accounted for under the cost-to-cost method, for which the recorded amounts require estimates of costs to complete and the amount of variable consideration included in the contract transaction price; allowances for doubtful accounts; fair value estimates, including those related to business acquisitions, valuations of goodwill and intangible assets, acquisition-related contingent consideration and equity investments; asset lives used in computing depreciation and amortization; fair values of financial instruments; self-insurance liabilities; other accruals and allowances; income taxes; and the estimated effects of litigation and other contingencies. While management believes that such estimates are reasonable when considered in conjunction with the Company’s consolidated financial position and results of operations taken as a whole, actual results could differ materially from those estimates.
Revenue Recognition	Revenue Recognition The Company adopted the requirements of Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers, which is also referred to as Accounting Standards Codification (“ASC”) Topic 606 (“Topic 606”), under the modified retrospective transition approach effective January 1, 2018, with application to all existing contracts that were not substantially completed as of January 1, 2018. The difference between the recognition criteria under Topic 606 and the Company’s previous revenue recognition practices under the previous revenue recognition guidance, ASC Topic 605-35, was recognized through a cumulative effect adjustment of approximately $2 million that was made to the opening balance of retained earnings as of January 1, 2018. Consistent with the modified retrospective transition approach, the comparative 2017 prior period was not adjusted to conform to the current period presentation. Under Topic 606, revenue is recognized when, or as, control of promised goods and services is transferred to customers, and the amount of revenue recognized reflects the consideration to which an entity expects to be entitled in exchange for the goods and services transferred. The adoption of Topic 606 did not have, and is not expected to have, a material effect on the timing or amount of revenue recognized as compared with the Company’s previous revenue recognition practices. Revenue is recognized by the Company primarily over time utilizing the cost-to-cost measure of progress, which is an input method, for fixed price contracts and certain master service and other service agreements, consistent with the Company’s previous revenue recognition practices. Under Topic 606, the cost-to-cost measure of progress best depicts the continuous transfer of control of goods or services to the customer, and correspondingly, when performance obligations are satisfied, for these contracts. Contracts. The Company derives revenue primarily from construction projects performed: i) under master and other service agreements, which provide a menu of available services in a specific geographic territory that are utilized on an as-needed basis, and are typically priced using time and materials or a fixed price per unit basis; or ii) under contracts for specific projects requiring the construction and installation of an entire infrastructure system or specified units within an infrastructure system, which are subject to multiple pricing options, including fixed price, unit price, time and materials, or cost plus a markup. Revenue derived from master service and other service agreements totaled 32% of consolidated revenue for both the three month periods ended September 30, 2018 and 2017, and totaled 36% and 35% for the nine month periods ended September 30, 2018 and 2017, respectively. Fixed price contracts provide for a fixed amount of revenue for the entire project. Revenue from these contracts, as well as for certain projects pursuant to master and other service agreements, is recognized over time using the cost-to-cost measure of progress. For these contracts, the cost-to-cost measure of progress best depicts the continuous transfer of control of goods or services to the customer. Such contracts provide that the customer accept completion of progress to date and compensate the Company for services rendered. For certain of the Company’s master service and other service agreements, under which it performs installation and maintenance services, primarily for install-to-the-home service providers in its Communications segment, revenue is recognized at a point in time. This is generally when the work order has been fulfilled, which is typically the same day the work is initiated. Point in time revenue accounted for approximately 6% and 7% of consolidated revenue for the three and nine month periods ended September 30, 2018, respectively. Substantially all of the Company’s other revenue is recognized over time. Contract costs include all direct materials, labor and subcontracted costs, as well as indirect costs related to contract performance, such as indirect labor, supplies, tools, repairs and the operational costs of capital equipment. The cost estimation process for recognizing revenue over time under the cost-to-cost method is based on the professional knowledge and experience of the Company’s project managers, engineers and financial professionals. Management reviews estimates of total contract transaction price and total project costs on an ongoing basis. Changes in job performance, job conditions and management’s assessment of expected variable consideration are factors that influence estimates of the total contract transaction price, total costs to complete those contracts and the Company’s profit recognition. Changes in these factors could result in revisions to revenue in the period in which the revisions are determined, which could materially affect the Company’s consolidated results of operations for that period. Provisions for losses on uncompleted contracts are recorded in the period in which such losses are determined. For both the nine month periods ended September 30, 2018 and 2017, project profit was affected by less than 5% as a result of changes in contract estimates included in projects that were in process as of December 31, 2017 and 2016. Revenue recognized for the three and nine month periods ended September 30, 2018 from performance obligations satisfied, or work completed, in prior periods totaled approximately $72.7 million and $55.6 million, respectively, which represents the effect on revenue for the periods presented of changes in transaction prices from variable consideration on certain projects. The Company may incur certain costs, such as initial set-up or mobilization costs, that can be capitalized. Such costs were not material for the three and nine month periods ended September 30, 2018. The timing of customer billings is generally dependent upon advance billing terms, milestone billings based on the completion of certain phases of the work, or when services are provided. Under the typical payment terms of master and other service agreements and fixed price contracts, the customer makes progress payments based on quantifiable measures of performance by the Company as defined by each specific agreement. Progress payments, generally net of amounts retained, are paid by the customer over the duration of the contract. For install-to-the-home contracts, work orders are billed and paid as completed. Amounts billed and due from customers, as well as the amount of contract assets, are classified within accounts receivable, net, in the consolidated balance sheets. See Note 5 - Accounts Receivable, Net of Allowance, and Contract Assets and Liabilities for related discussion. Amounts expected to be collected beyond one year are classified as other long-term assets. Performance Obligations. A performance obligation is a contractual promise to transfer a distinct good or service to a customer, and is the unit of account under Topic 606. The transaction price of a contract is allocated to each distinct performance obligation and recognized as revenue when or as the performance obligation is satisfied. The Company’s contracts often require significant services to integrate complex activities and equipment into a single deliverable, and are therefore generally accounted for as a single performance obligation, even when delivering multiple distinct services. Contract amendments and change orders are generally not distinct from the existing contract and are accounted for as a modification of the existing contract and performance obligation. The majority of the Company’s performance obligations are completed within one year. When more than one contract is entered into with a customer on or close to the same date, the Company evaluates whether those contracts should be combined and accounted for as a single contract as well as whether those contracts should be accounted for as one, or more than one, performance obligation. This evaluation requires significant judgment and is based on the facts and circumstances of the various contracts. Remaining performance obligations represent the amount of unearned transaction prices under contracts for which work is wholly or partially unperformed, including the Company’s share of unearned transaction prices from its proportionately consolidated non-controlled joint ventures. As of September 30, 2018, the amount of the Company’s remaining performance obligations was $5.3 billion. The Company expects to recognize approximately $1.7 billion of its remaining performance obligations as revenue during the remainder of 2018, with the majority of the balance to be recognized in 2019. Variable Consideration. Transaction prices for the Company’s contracts may include variable consideration, which comprises items such as change orders, claims, incentives and liquidated damages. Management estimates variable consideration for a performance obligation utilizing estimation methods that best predict the amount of consideration to which the Company will be entitled. Variable consideration is included in the estimated transaction price to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Management’s estimates of variable consideration and determination of whether to include estimated amounts in transaction price are based largely on engineering studies and legal opinions, past practices with the customer, specific discussions, correspondence or preliminary negotiations with the customer and all other relevant information that is reasonably available. The effect of variable consideration on the transaction price of a performance obligation is typically recognized as an adjustment to revenue on a cumulative catch-up basis, as such variable consideration, which typically pertains to changed conditions and scope, is generally for services encompassed under the existing contract. To the extent unapproved change orders, claims and liquidated damages reflected in transaction prices are not resolved in the Company’s favor, or to the extent incentives reflected in transaction prices are not earned, there could be reductions in, or reversals of, previously recognized revenue. As of September 30, 2018 and December 31, 2017, the Company included approximately $56 million and $146 million, respectively, of change orders and/or claims in the transaction price for certain contracts that were in the process of being resolved in the normal course of business, including through negotiation, arbitration and other proceedings. These transaction price adjustments are included within costs and earnings in excess of billings or accounts receivable, net of allowance, as appropriate. As of both September 30, 2018 and December 31, 2017, these change orders and/or claims were primarily related to certain large long-haul pipeline construction projects in the Oil and Gas segment. The Company actively engages with its customers to complete the final approval process, and generally expects these processes to be completed within one year. Amounts ultimately realized upon final acceptance by customers could be higher or lower than such estimated amounts.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements See the revenue recognition discussion within Significant Accounting Policies above, and the recent accounting pronouncements discussion below, for information pertaining to the effects of recently adopted and other recent accounting pronouncements, as updated from the discussion in the Company’s 2017 Form 10-K. Other Accounting Pronouncements Adopted in 2018 In August 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”) to reduce diversity in practice by providing guidance on the classification of certain cash receipts and payments in the statement of cash flows. This ASU, which the Company adopted as of January 1, 2018, is effective on a retrospective basis, and resulted in the reclassification of certain types of activity in the consolidated statement of cash flows, including the reclassification of $12 million of second quarter 2017 acquisition-related contingent consideration payments in excess of acquisition date liabilities from financing to operating cash flows. Additionally, in connection with the adoption of this ASU, the Company elected to account for distributions received from equity method investees using the nature of distributions approach, under which distributions are classified based on the nature of the activity that generated them. The other provisions of this ASU did not have a material effect on the Company’s consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”), which was further amended in February and in March 2018 by ASU 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2018-03”) and ASU 2018-04, Investments - Debt Securities (Topic 320) and Regulated Operations (Topic 980):Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 117 and SEC Release No. 33-9273 (“ASU 2018-04”) to clarify certain aspects of ASU 2016-01 and to update Securities and Exchange Commission (“SEC”) interpretive guidance in connection with the provisions of ASU 2016-01. These ASUs provide guidance for the recognition, measurement, presentation and disclosure of financial assets and financial liabilities, including equity investments other than those accounted for under the equity method of accounting or those that are consolidated. Equity investments within the scope of these ASUs are required to be measured at fair value with changes in fair value recognized in net income. Equity investments that do not have readily determinable fair values are permitted to be measured at cost, less any impairment, plus or minus any changes resulting from observable price changes for identical or similar investments of the same issuer (the “measurement alternative”). The Company adopted these ASUs as of January 1, 2018, which was applicable to the Company on a prospective basis, as the Company’s equity investments for which it elected to utilize the measurement alternative, do not have readily determinable fair values. The adoption of these ASUs will result in volatility in other income (expense), net, upon the occurrence of future observable price changes or impairments related to these investments. For further information pertaining to the Company’s equity investments, see Note 4 - Fair Value of Financial Instruments. The other provisions of these ASUs did not have a material effect on the Company’s consolidated financial statements. Other Recent Accounting Pronouncements In August 2018, the SEC issued Release No. 33-10532, Disclosure Update and Simplification, which amends and clarifies certain financial reporting disclosure requirements. The principal change from this new guidance will be the inclusion of a statement of changes in shareholders' equity in the Company’s interim consolidated financial statements beginning with the quarter ended March 31, 2019. 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 (“ASU 2018-15”) to reduce diversity in practice in accounting for the costs of implementing cloud computing arrangements that are service contracts. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for internal-use software. Accounting for the service element of the cloud computing arrangement is not affected by the new guidance. Under ASU 2018-15, amortization expense, payments for and asset balances related to such capitalized implementation costs are to be presented within the same line items of the entity’s statements of operations, cash flows and balance sheets, respectively, as the related service fee activity and balances would be presented. ASU 2018-15 is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the effect of this ASU on its consolidated financial statements. 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 (“ASU 2018-13”). ASU 2018-13, which is intended to improve the effectiveness of fair value measurement disclosures, modifies the disclosure requirements for certain estimates and assumptions used in determining the fair value of assets and liabilities. ASU 2018-13 is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the effect of this ASU on its consolidated financial statements. In June 2018, the FASB issued ASU 2018-07, Compensation-Stock Compensation (Topic 718) - Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 expands the guidance in Topic 718 to include share-based payments for goods and services to non-employees and generally aligns it with the guidance for share-based payments to employees. ASU 2018-07 is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company is currently evaluating the effect of this ASU on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”), which was further clarified and amended in July 2018 by ASU 2018-10, Codification Improvements to Topic 842, Leases (“ASU 2018-10”) and ASU 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”). These ASUs provide revised guidance for lease accounting and related disclosure requirements, including a requirement for lessees to recognize right-of use assets and lease liabilities on the balance sheet for leases with durations greater than twelve months. The new guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018, with early adoption permitted. The Company will adopt these ASUs as of January 1, 2019, and expects to adopt the new guidance using the transition method that allows entities to initially apply the new standard as of the date of adoption and recognize a cumulative effect adjustment to the opening balance of retained earnings as of that date. In addition, the Company expects to utilize the package of practical expedients that allows entities to retain the classification of lease contracts existing as of the date of adoption. The Company is continuing to assess and quantify the potential effects of the new guidance on its consolidated financial statements, business processes, systems and controls. The Company’s assessment, which it expects to substantially complete in the fourth quarter of 2018, includes an evaluation of its existing lease portfolio, a comparison of its historical accounting policies and practices to the new standard, and an evaluation of the effect of certain accounting policy elections. The Company is in the process of implementing a new lease accounting and administration software solution in connection with the new standard, and is currently evaluating certain changes to its business processes and internal controls to meet the reporting and disclosure requirements of the new standard. The new guidance is not expected to materially affect the amount of expense recognized under the Company’s current leasing arrangements, however, based on its review to date of existing lease contracts, the amount of incremental lease assets and liabilities to be recognized on its consolidated balance sheets upon adoption is expected to be material. The Company’s expectations may change as its assessment progresses. For information about the Company’s future lease commitments as of December 31, 2017, see Note 8 - Lease Obligations, in the Company’s 2017 Form 10-K.