Commitments and Contingencies (Other Guarantees) (Narrative) (Details)	9 Months Ended
	Sep. 30, 2018
Other Guarantees [Line Items]
General warranty, description	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.
Minimum [Member]
Other Guarantees [Line Items]
General warranty, period (in years)	1 year
Maximum [Member]
Other Guarantees [Line Items]
General warranty, period (in years)	2 years
Subsidiaries [Member]
Other Guarantees [Line Items]
Other guarantees, description	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.