Goodwill and Other Intangible Assets (Unaudited Pro Forma Financial Information) (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Combinations, Unaudited Pro Forma Information [Abstract]
Business combinations, unaudited pro forma revenue	$ 1,977.2	$ 1,964.8	$ 4,994.9	$ 5,109.0
Business combinations, unaudited pro forma net income	121.0	63.5	$ 225.6	190.6
Business combinations, unaudited pro forma information, description			These unaudited pro forma financial results represent the results of operations of the companies acquired as if the acquired companies had been consolidated as of the beginning of the year prior to their acquisition, and are provided for illustrative purposes only. These unaudited pro forma financial results 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 Company’s unaudited pro forma financial results were prepared by adjusting the historical results of MasTec to include the unaudited historical results of the acquired businesses described above, and then adjusted for (i) acquisition costs; (ii) amortization expense resulting from the acquired intangible assets; (iii) interest expense as a result of the cash consideration paid; (iv) interest expense from debt repaid upon acquisition; and (iv) elimination of the effects of intercompany transactions and other purchase accounting related adjustments. These unaudited pro forma financial results do not include adjustments to reflect other cost savings or synergies that may have resulted from these acquisitions.
Business combinations, acquisition-related results, revenue	18.4	62.2	$ 141.0	96.1
Business combinations, acquisition-related results, net income (loss)	$ (0.9)	$ 3.2	$ 1.9	$ 4.7