Goodwill and Other Intangible Assets (2017 Acquisitions) (Narrative) (Details) $ in Millions		12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Combinations [Line Items]
Business combinations, number of acquisitions		3
Business combinations, unaudited pro forma revenue (in dollars)		$ 6,680.2	$ 5,320.1
Business combinations, unaudited pro forma net income (in dollars)		$ 354.9	$ 140.0
Business combinations, unaudited pro forma information, description		The above indicated unaudited pro forma financial results, which represent the results of operations of the companies acquired as if the acquired companies had been consolidated as of January 1, 2016, are provided for illustrative purposes only and do not purport to be indicative of the actual results that would have been achieved by the combined companies for the periods indicated, or of the results that may be achieved by the combined companies in the future. The unaudited supplemental pro forma financial results have been prepared by adjusting the historical results of MasTec to include the historical results of the acquired businesses described above, and then adjusted (i) to remove acquisition costs; (ii) to increase amortization expense resulting from the acquired intangible assets; (iii) to increase interest expense as a result of the cash consideration paid; (iv) to reduce interest expense from debt repaid upon acquisition; and (iv) to eliminate the effects of intercompany transactions. These unaudited supplemental pro forma financial results do not include adjustments to reflect other cost savings or synergies that may have resulted from these acquisitions.
Business combinations, consolidated acquisition-related results, revenue (in dollars)		$ 160.1
Business combinations, consolidated acquisition-related results, net income (in dollars)		$ 10.2
Earn-Out Liabilities [Member]
Business Combinations [Line Items]
Business combinations, contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited		there is no maximum payment amount
2017 Acquisitions [Member]
Business Combinations [Line Items]
Business combinations, percentage of interests acquired	100.00%	100.00%
Business combinations, acquired finite-lived intangible assets, weighted average lives (in years)		10 years
Business combinations, goodwill recognized, description		The goodwill balances for the respective acquisitions represent the estimated value of each acquired company’s geographic presence in key markets, its assembled workforce and management team industry-specific project management expertise, as well as synergies expected to be achieved from the combined operations of the acquired companies and MasTec.
Business combinations, goodwill, expected tax deductible amount (in dollars)	$ 75.0	$ 75.0
2017 Acquisitions [Member] | Earn-Out Liabilities [Member]
Business Combinations [Line Items]
Business combinations, contingent consideration, basis for amount		The contingent consideration included in the table above equals the acquired companies’ earnings before interest, taxes, depreciation and amortization (“EBITDA”) above certain thresholds, if applicable, for a period of five years, as set forth in the respective purchase agreements, which amounts are payable annually.
Contingent consideration, earn-out period		5 years
Business combinations, contingent consideration, fair value measurements, valuation technique		The fair values of the earn-out liabilities were estimated using income approaches such as discounted cash flows or option pricing models and incorporate significant inputs not observable in the market.
Fair value measurements, significant assumptions		Key assumptions in the estimated valuations include the discount rate and probability-weighted EBITDA projections.
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, low	9.0	$ 9.0
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high	$ 185.0	$ 185.0
Business combinations, contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited		there is no maximum payment amount
2017 Acquisitions [Member] | Customer Relationships [Member]
Business Combinations [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average lives (in years)	11 years
2017 Acquisitions [Member] | Backlog [Member]
Business Combinations [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average lives (in years)	4 years
2017 Acquisitions [Member] | Other Amortizing Intangible Assets [Member]
Business Combinations [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average lives (in years)	7 years
2017 Communications Acquisition [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity		a wireline/fiber deployment construction contractor
2017 Power Generation and Industrial Acquisition [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity		a heavy civil construction services company
2017 Oil and Gas Acquisition [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity		an oil and gas pipeline equipment company