Goodwill and Other Intangible Assets (2017 Acquisitions) (Narrative) (Details) $ in Millions		3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Business Combination [Line Items]
Business combinations, number of acquisitions				3
Unaudited Pro Forma Financial Information and Aquisition-Related Results
Business acquisition, pro forma revenue		$ 1,955.8	$ 1,634.5	$ 5,077.4	$ 3,934.6
Business acquisition, pro forma net income		64.4	$ 59.0	$ 192.0	$ 81.5
Business acquisition, pro forma information, description				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 effect of intercompany transactions. Additionally, the 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 acquisition, acquisition-related results, revenue		62.2		$ 96.1
Business acquisition, acquisition-related results, net income		3.2		$ 4.7
2017 Communications Acquisition [Member]
Business Combination [Line Items]
Business combinations, description of acquired entity				a wireline/fiber deployment construction contractor
2017 Power Generation and Industrial Acquisition [Member]
Business Combination [Line Items]
Business combinations, description of acquired entity				a heavy civil construction services company
2017 Oil and Gas Acquisition [Member]
Business Combination [Line Items]
Business combinations, description of acquired entity				an oil and gas pipeline equipment company
2017 Acquisitions [Member]
Business Combination [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average useful life (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, their 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		$ 75.0
2017 Acquisitions [Member] | Earn-Out Arrangements [Member]
Business Combination [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 (in years)				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.
Business combinations, contingent consideration, fair value measurements, significant assumptions				Key assumptions in the estimated valuations include the discount rate and probability-weighted EBITDA projections.
2017 Acquisitions [Member] | Customer Relationships [Member]
Business Combination [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average useful life (in years)	11 years
2017 Acquisitions [Member] | Backlog [Member]
Business Combination [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average useful life (in years)	4 years
2017 Acquisitions [Member] | Other Amortizing Intangible Assets [Member]
Business Combination [Line Items]
Business combinations, acquired finite-lived intangible assets, weighted average useful life (in years)	7 years