Commitments and Contingencies	12 Months Ended
Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 14 - Commitments and Contingencies MasTec is subject to a variety of legal cases, claims and other disputes that arise from time to time in the ordinary course of its business. MasTec cannot provide assurance that it will be successful in recovering all or any of the potential damages it has claimed or in defending claims against the Company. The outcome of such cases, claims and disputes cannot be predicted with certainty and an unfavorable resolution of one or more of them could have a material adverse effect on the Company’s business, financial condition, results of operations and cash flows. Other Commitments and Contingencies Leases. In the ordinary course of business, the Company enters into non-cancelable operating leases for certain of its facility, vehicle and equipment needs, including related party leases. See Note 8 - Lease Obligations and Note 15 - Related Party Transactions. Letters of Credit. In the ordinary course of business, the Company is required to post letters of credit for its insurance carriers, surety bond providers and in support of performance under certain contracts as well as certain obligations associated with the Company’s equity investments, including its variable interest entities. Such letters of credit are generally issued by a bank or similar financial institution. The letter of credit commits the issuer to pay specified amounts to the holder of the letter of credit under certain conditions. If this were to occur, the Company would be required to reimburse the issuer of the letter of credit, which, depending upon the circumstances, could result in a charge to earnings. As of December 31, 2017 and 2016, there were $157.1 million and $314.3 million, respectively, of letters of credit issued under the Company’s Credit Facility. The Company is not aware of material claims relating to its outstanding letters of credit as of December 31, 2017 or 2016. Performance and Payment Bonds. In the ordinary course of business, MasTec is required by certain customers to provide performance and payment bonds for contractual commitments related to projects in process. These bonds provide a guarantee to the customer that the Company will perform under the terms of a contract and that the Company will pay subcontractors and vendors. If the Company fails to perform under a contract or to pay subcontractors and vendors, the customer may demand that the surety make payments or provide services under the bond. The Company must reimburse the surety for expenses or outlays it incurs. As of December 31, 2017 and 2016, outstanding performance and payment bonds totaled $119.7 million and $72.9 million, respectively, and estimated costs to complete projects secured by these bonds totaled $46.0 million and $9.5 million, respectively. These amounts do not include performance and payment bonds associated with the Company’s equity investments. Investment Arrangements. From time to time, the Company may participate in selected investment or strategic arrangements to expand its operations, customer base or geographic reach, including arrangements that combine the Company’s skills and resources with those of others to allow for the performance of particular projects. The Company holds undivided interests, ranging from 85% to 90%, in several proportionately consolidated non-controlled contractual joint ventures that provide infrastructure construction services for electrical transmission projects. The Company also holds a 35% undivided interest in a proportionately consolidated non-controlled Canadian contractual joint venture that was underway when the Company acquired Pacer in 2014, whose sole activity involves the construction of a bridge, a business in which the Company does not otherwise engage. This joint venture, which is managed by a third party, and for which the Company has minimal direct construction involvement, automatically terminates upon completion of the project. Income and/or losses incurred by these joint ventures are generally shared proportionally by the respective joint venture members, with the members of the joint ventures jointly and severally liable for all of the obligations of the joint venture. The respective joint venture agreements provide that each joint venture partner indemnify the other party for any liabilities incurred by such joint venture in excess of its ratable portion of such liabilities. Thus, it is possible that the Company could be required to pay or perform obligations in excess of its share if the other joint venture partners fail or refuse to pay or perform their respective share of the obligations. As of December 31, 2017, the Company was not aware of circumstances that would reasonably lead to material future claims against it in connection with these arrangements. The Company has other investment arrangements, as discussed in Note 4 - Fair Value of Financial Instruments and Note 15 - Related Party Transactions. The Company may incur costs or provide financing, performance, financial and/or other guarantees to or in connection with these arrangements. Self-Insurance. MasTec maintains insurance policies for workers’ compensation, general liability and automobile liability, which are subject to per claim deductibles. The Company is self-insured up to the amount of the deductible. The Company also maintains excess umbrella coverage. As of December 31, 2017 and 2016, MasTec’s liability for unpaid claims and associated expenses, including incurred but not reported losses related to these policies, totaled $106.2 million and $85.8 million, respectively, of which $72.2 million and $55.2 million, respectively, were reflected within other long-term liabilities in the consolidated balance sheets. MasTec also maintains an insurance policy with respect to employee group medical claims, which is subject to annual per employee maximum losses. MasTec’s liability for employee group medical claims totaled $2.6 million as of both December 31, 2017 and 2016. The Company is required to post letters of credit and provide cash collateral to certain of its insurance carriers and to provide surety bonds in certain states. Insurance-related letters of credit for the Company’s workers’ compensation, general liability and automobile liability policies amounted to $88.9 million and $85.1 million as of December 31, 2017 and 2016, respectively. In addition, cash collateral deposited with insurance carriers, which is included within other long-term assets, amounted to $1.6 million and $1.5 million for these policies as of December 31, 2017 and 2016, respectively. Outstanding surety bonds related to workers’ compensation self-insurance programs amounted to $15.2 million and $13.5 million as of December 31, 2017 and 2016, respectively. Employment Agreements. The Company has employment agreements with certain executives and other employees, which provide for compensation and certain other benefits and for severance payments under certain circumstances. Certain employment agreements also contain clauses that become effective upon a change in control of the Company. Upon the occurrence of any of the defined events in the various employment agreements, the Company would be obligated to pay certain amounts to the relevant employees, which vary with the level of the employees’ respective responsibility. Collective Bargaining Agreements and Multiemployer Plans. As discussed in Note 1 - Business, Basis of Presentation and Significant Accounting Policies, certain of MasTec’s subsidiaries are party to various collective bargaining agreements with unions representing certain of their employees, which require the Company to pay specified wages, provide certain benefits to their union employees and contribute certain amounts to MEPPs. The Employee Retirement Income Security Act of 1974, as amended by the Multiemployer Pension Plan Amendments Act of 1980 (collectively, “ERISA”), which governs U.S.-registered multiemployer pension plans, subjects employers to substantial liabilities in the event of the employer’s complete or partial withdrawal from, or upon termination of, such plans. The Company currently contributes, and in the past has contributed to, plans that are underfunded, and, therefore, could have potential liability associated with a voluntary or involuntary withdrawal from, or termination of, these plans. In November 2014, the Company, along with other members of the Pipe Line Contractors Association (the “PLCA”), voluntarily terminated its participation in several MEPPs. Additionally, the Company, along with other members of the PLCA, voluntarily withdrew from the Central States Southeast and Southwest Areas Pension Fund (“Central States”) in 2011, for which the Company established and paid a $6.4 million withdrawal liability. During the year ended December 31, 2017, the Company recognized $0.7 million of expense in connection with the expected final settlement of this matter. The Company does not have plans to withdraw from, and is not aware of circumstances that would reasonably lead to material claims against it, in connection with its participation in any other plans. However, there can be no assurance that the Company will not be assessed liabilities in the future. Based upon the information available to the Company from plan administrators as of December 31, 2017, several of the MEPPs in which it participates are underfunded and, as a result, the Company could be required to increase its contributions, including in the form of a surcharge on future benefit contributions. The amount of additional funds the Company may be obligated to contribute in the future cannot be estimated, as these amounts are based on future levels of work of the union employees covered by these plans, investment returns and the level of underfunding of such plans. Indemnities. The Company generally indemnifies its customers for the services it provides under its contracts, as well as other specified liabilities, which may subject the Company to indemnity claims, liabilities and related litigation. As of December 31, 2017 and 2016, the Company was not aware of any material asserted or unasserted claims in connection with these indemnity obligations. Other Guarantees. In the ordinary course of its business, from time to time, MasTec guarantees the obligations of its subsidiaries, including obligations under certain contracts with customers, certain lease obligations and in some states, obligations in connection with obtaining contractors’ licenses. MasTec has also issued performance and other guarantees in connection with certain of its equity investments. MasTec also generally warrants the work it performs for a one to two year period following substantial completion of a project. Much of the work performed by the Company is evaluated for defects shortly after the work is completed. Accrued warranty claims are, and historically have been, de minimis. However, if warranty claims occur, the Company could be required to repair or replace warrantied items, or, if customers elect to repair or replace the warrantied item using the services of another provider, the Company could be required to pay for the cost of the repair or replacement. Concentrations of Risk. The Company is subject to certain risk factors, including, but not limited to: risks related to customer consolidation, rapid technological and regulatory changes; changes in customers’ capital spending plans; risks related to market conditions and/or economic downturns; competition; the ability to manage projects effectively and in accordance with management’s estimates; customer disputes related to the performance of services; the nature of its contracts, which do not obligate MasTec’s customers to undertake any infrastructure projects and may be canceled on short notice; seasonality, adverse weather conditions and fluctuations in operational factors; risks related to the Company’s acquisitions and investment arrangements, including acquisition integration and financing; recoverability of goodwill; governmental and/or regulatory changes or other factors affecting the industries in which the Company operates; potential exposure to environmental liabilities; collectibility of receivables; exposure from system or information technology interruptions; availability of qualified employees; the adequacy of our reserves; exposure to litigation; exposure related to foreign operations; and exposure to multiemployer pension plan liabilities. The Company grants credit, generally without collateral, to its customers. Consequently, the Company is subject to potential credit risk related to changes in business and economic factors. However, MasTec generally has certain lien rights on that work and maintains a diverse customer base. The Company believes its billing and collection policies are adequate to minimize potential credit risk. MasTec’s customers include: public and private energy providers; pipeline operators; wireless and wireline/fiber service providers; broadband operators; install-to-the-home service providers; and government entities. The industries served by MasTec’s customers include, among others: communications; and utilities (including petroleum and natural gas pipeline infrastructure; electrical utility transmission and distribution; power generation; heavy civil and industrial infrastructure). The Company had approximately 500 customers for the year ended December 31, 2017. As of December 31, 2017 and 2016, one customer accounted for approximately 46% and 24%, respectively, of the Company’s consolidated net accounts receivable position, which represents accounts receivable, net, less BIEC. As of December 31, 2017 and 2016, a separate customer accounted for approximately 15% and 17%, respectively, of the Company’s consolidated net accounts receivable position. In addition, the Company derived 78%, 76% and 61%, of its revenue from its top ten customers for the years ended December 31, 2017, 2016 and 2015, respectively.

Note 14 - Commitments and Contingencies

MasTec is subject to a variety of legal cases, claims and other disputes that arise from time to time in the ordinary course of its business. MasTec cannot provide assurance that it will be successful in recovering all or any of the potential damages it has claimed or in defending claims against the Company. The outcome of such cases, claims and disputes cannot be predicted with certainty and an unfavorable resolution of one or more of them could have a material adverse effect on the Company’s business, financial condition, results of operations and cash flows.

Other Commitments and Contingencies

Leases. In the ordinary course of business, the Company enters into non-cancelable operating leases for certain of its facility, vehicle and equipment needs, including related party leases. See Note 8 - Lease Obligations and Note 15 - Related Party Transactions.

Letters of Credit. In the ordinary course of business, the Company is required to post letters of credit for its insurance carriers, surety bond providers and in support of performance under certain contracts as well as certain obligations associated with the Company’s equity investments, including its variable interest entities. Such letters of credit are generally issued by a bank or similar financial institution. The letter of credit commits the issuer to pay specified amounts to the holder of the letter of credit under certain conditions. If this were to occur, the Company would be required to reimburse the issuer of the letter of credit, which, depending upon the circumstances, could result in a charge to earnings. As of December 31, 2017 and 2016, there were $157.1 million and $314.3 million, respectively, of letters of credit issued under the Company’s Credit Facility. The Company is not aware of material claims relating to its outstanding letters of credit as of December 31, 2017 or 2016.

Performance and Payment Bonds. In the ordinary course of business, MasTec is required by certain customers to provide performance and payment bonds for contractual commitments related to projects in process. These bonds provide a guarantee to the customer that the Company will perform under the terms of a contract and that the Company will pay subcontractors and vendors. If the Company fails to perform under a contract or to pay subcontractors and vendors, the customer may demand that the surety make payments or provide services under the bond. The Company must reimburse the surety for expenses or outlays it incurs. As of December 31, 2017 and 2016, outstanding performance and payment bonds totaled $119.7 million and $72.9 million, respectively, and estimated costs to complete projects secured by these bonds totaled $46.0 million and $9.5 million, respectively. These amounts do not include performance and payment bonds associated with the Company’s equity investments.

Investment Arrangements. From time to time, the Company may participate in selected investment or strategic arrangements to expand its operations, customer base or geographic reach, including arrangements that combine the Company’s skills and resources with those of others to allow for the performance of particular projects. The Company holds undivided interests, ranging from 85% to 90%, in several proportionately consolidated non-controlled contractual joint ventures that provide infrastructure construction services for electrical transmission projects. The Company also holds a 35% undivided interest in a proportionately consolidated non-controlled Canadian contractual joint venture that was underway when the Company acquired Pacer in 2014, whose sole activity involves the construction of a bridge, a business in which the Company does not otherwise engage. This joint venture, which is managed by a third party, and for which the Company has minimal direct construction involvement, automatically terminates upon completion of the project. Income and/or losses incurred by these joint ventures are generally shared proportionally by the respective joint venture members, with the members of the joint ventures jointly and severally liable for all of the obligations of the joint venture. The respective joint venture agreements provide that each joint venture partner indemnify the other party for any liabilities incurred by such joint venture in excess of its ratable portion of such liabilities. Thus, it is possible that the Company could be required to pay or perform obligations in excess of its share if the other joint venture partners fail or refuse to pay or perform their respective share of the obligations. As of December 31, 2017, the Company was not aware of circumstances that would reasonably lead to material future claims against it in connection with these arrangements.

The Company has other investment arrangements, as discussed in Note 4 - Fair Value of Financial Instruments and Note 15 - Related Party Transactions. The Company may incur costs or provide financing, performance, financial and/or other guarantees to or in connection with these arrangements.

Self-Insurance. MasTec maintains insurance policies for workers’ compensation, general liability and automobile liability, which are subject to per claim deductibles. The Company is self-insured up to the amount of the deductible. The Company also maintains excess umbrella coverage. As of December 31, 2017 and 2016, MasTec’s liability for unpaid claims and associated expenses, including incurred but not reported losses related to these policies, totaled $106.2 million and $85.8 million, respectively, of which $72.2 million and $55.2 million, respectively, were reflected within other long-term liabilities in the consolidated balance sheets. MasTec also maintains an insurance policy with respect to employee group medical claims, which is subject to annual per employee maximum losses. MasTec’s liability for employee group medical claims totaled $2.6 million as of both December 31, 2017 and 2016.

The Company is required to post letters of credit and provide cash collateral to certain of its insurance carriers and to provide surety bonds in certain states. Insurance-related letters of credit for the Company’s workers’ compensation, general liability and automobile liability policies amounted to $88.9 million and $85.1 million as of December 31, 2017 and 2016, respectively. In addition, cash collateral deposited with insurance carriers, which is included within other long-term assets, amounted to $1.6 million and $1.5 million for these policies as of December 31, 2017 and 2016, respectively. Outstanding surety bonds related to workers’ compensation self-insurance programs amounted to $15.2 million and $13.5 million as of December 31, 2017 and 2016, respectively.

Employment Agreements. The Company has employment agreements with certain executives and other employees, which provide for compensation and certain other benefits and for severance payments under certain circumstances. Certain employment agreements also contain clauses that become effective upon a change in control of the Company. Upon the occurrence of any of the defined events in the various employment agreements, the Company would be obligated to pay certain amounts to the relevant employees, which vary with the level of the employees’ respective responsibility.

Collective Bargaining Agreements and Multiemployer Plans. As discussed in Note 1 - Business, Basis of Presentation and Significant Accounting Policies, certain of MasTec’s subsidiaries are party to various collective bargaining agreements with unions representing certain of their employees, which require the Company to pay specified wages, provide certain benefits to their union employees and contribute certain amounts to MEPPs. The Employee Retirement Income Security Act of 1974, as amended by the Multiemployer Pension Plan Amendments Act of 1980 (collectively, “ERISA”), which governs U.S.-registered multiemployer pension plans, subjects employers to substantial liabilities in the event of the employer’s complete or partial withdrawal from, or upon termination of, such plans.

The Company currently contributes, and in the past has contributed to, plans that are underfunded, and, therefore, could have potential liability associated with a voluntary or involuntary withdrawal from, or termination of, these plans. In November 2014, the Company, along with other members of the Pipe Line Contractors Association (the “PLCA”), voluntarily terminated its participation in several MEPPs. Additionally, the Company, along with other members of the PLCA, voluntarily withdrew from the Central States Southeast and Southwest Areas Pension Fund (“Central States”) in 2011, for which the Company established and paid a $6.4 million withdrawal liability. During the year ended December 31, 2017, the Company recognized $0.7 million of expense in connection with the expected final settlement of this matter. The Company does not have plans to withdraw from, and is not aware of circumstances that would reasonably lead to material claims against it, in connection with its participation in any other plans. However, there can be no assurance that the Company will not be assessed liabilities in the future.

Based upon the information available to the Company from plan administrators as of December 31, 2017, several of the MEPPs in which it participates are underfunded and, as a result, the Company could be required to increase its contributions, including in the form of a surcharge on future benefit contributions. The amount of additional funds the Company may be obligated to contribute in the future cannot be estimated, as these amounts are based on future levels of work of the union employees covered by these plans, investment returns and the level of underfunding of such plans.

Indemnities. The Company generally indemnifies its customers for the services it provides under its contracts, as well as other specified liabilities, which may subject the Company to indemnity claims, liabilities and related litigation. As of December 31, 2017 and 2016, the Company was not aware of any material asserted or unasserted claims in connection with these indemnity obligations.

Other Guarantees. In the ordinary course of its business, from time to time, MasTec guarantees the obligations of its subsidiaries, including obligations under certain contracts with customers, certain lease obligations and in some states, obligations in connection with obtaining contractors’ licenses. MasTec has also issued performance and other guarantees in connection with certain of its equity investments. MasTec also generally warrants the work it performs for a one to two year period following substantial completion of a project. Much of the work performed by the Company is evaluated for defects shortly after the work is completed. Accrued warranty claims are, and historically have been, de minimis. However, if warranty claims occur, the Company could be required to repair or replace warrantied items, or, if customers elect to repair or replace the warrantied item using the services of another provider, the Company could be required to pay for the cost of the repair or replacement.

Concentrations of Risk. The Company is subject to certain risk factors, including, but not limited to: risks related to customer consolidation, rapid technological and regulatory changes; changes in customers’ capital spending plans; risks related to market conditions and/or economic downturns; competition; the ability to manage projects effectively and in accordance with management’s estimates; customer disputes related to the performance of services; the nature of its contracts, which do not obligate MasTec’s customers to undertake any infrastructure projects and may be canceled on short notice; seasonality, adverse weather conditions and fluctuations in operational factors; risks related to the Company’s acquisitions and investment arrangements, including acquisition integration and financing; recoverability of goodwill; governmental and/or regulatory changes or other factors affecting the industries in which the Company operates; potential exposure to environmental liabilities; collectibility of receivables; exposure from system or information technology interruptions; availability of qualified employees; the adequacy of our reserves; exposure to litigation; exposure related to foreign operations; and exposure to multiemployer pension plan liabilities. The Company grants credit, generally without collateral, to its customers. Consequently, the Company is subject to potential credit risk related to changes in business and economic factors. However, MasTec generally has certain lien rights on that work and maintains a diverse customer base. The Company believes its billing and collection policies are adequate to minimize potential credit risk. MasTec’s customers include: public and private energy providers; pipeline operators; wireless and wireline/fiber service providers; broadband operators; install-to-the-home service providers; and government entities. The industries served by MasTec’s customers include, among others: communications; and utilities (including petroleum and natural gas pipeline infrastructure; electrical utility transmission and distribution; power generation; heavy civil and industrial infrastructure). The Company had approximately 500 customers for the year ended December 31, 2017. As of December 31, 2017 and 2016, one customer accounted for approximately 46% and 24%, respectively, of the Company’s consolidated net accounts receivable position, which represents accounts receivable, net, less BIEC. As of December 31, 2017 and 2016, a separate customer accounted for approximately 15% and 17%, respectively, of the Company’s consolidated net accounts receivable position. In addition, the Company derived 78%, 76% and 61%, of its revenue from its top ten customers for the years ended December 31, 2017, 2016 and 2015, respectively.