Acquisitions (2014 Acquisitions - WesTower) (Narrative) (Details) - USD ($)		3 Months Ended				12 Months Ended
		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014	Oct. 01, 2014
Business Combinations [Line Items]
Business combinations, measurement period adjustments, goodwill increase (decrease)	[1]					$ (3,600,000)
Communications [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs		$ 1,200,000	$ 7,800,000	$ 8,800,000	$ 5,300,000	17,800,000		$ 5,300,000
Business combinations, measurement period adjustments, goodwill increase (decrease)	[1]					(3,600,000)
Communications [Member] | General and Administrative Expenses [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs						$ 17,800,000		5,300,000
WesTower [Member]
Business Combinations [Line Items]
Business combinations, effective date						Oct. 01, 2014
Business combinations, percentage of voting interests acquired						100.00%
Business combinations, name of acquired entity						WesTower Communications Inc. (“WesTower”)
Business combinations, description of acquired entity						a telecommunications services firm that focuses on construction and maintenance of communications infrastructure for wireless networks throughout the Eastern, Central and Western United States. The acquisition of WesTower has expanded the Company’s geographical presence, market penetration and skilled employee base within its existing wireless operations.
Business combinations, goodwill recognized, description						Goodwill arising from the acquisition represents the estimated value of WesTower’s geographic presence in key high growth markets, its assembled workforce and synergies expected to be achieved from the combined operations of WesTower and MasTec.
Business combinations, goodwill, expected tax deductible amount									$ 0
Business combinations, measurement period adjustments, goodwill increase (decrease)							$ (3,600,000)
WesTower [Member] | Long-Term Deferred Tax Liabilities [Member]
Business Combinations [Line Items]
Business combinations, measurement period adjustments, liabilities increase (decrease)							5,300,000
WesTower [Member] | Current Deferred Tax Assets [Member]
Business Combinations [Line Items]
Business combinations, measurement period adjustments, assets increase (decrease)							15,700,000
WesTower [Member] | Long-Term Deferred Tax Assets [Member]
Business Combinations [Line Items]
Business combinations, measurement period adjustments, assets increase (decrease)							$ (7,800,000)
WesTower [Member] | Current Liabilities [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs, current liabilities					$ 3,500,000	$ 1,500,000		3,500,000
WesTower [Member] | Communications [Member] | General and Administrative Expenses [Member]
Business Combinations [Line Items]
Business combinations, acquisition integration costs						$ 9,300,000		$ 5,000,000

[1] Represent adjustments to preliminary estimates of the fair values of net assets acquired within the measurement period. See Note 3 - Acquisitions for discussion of ASU 2015-16, which was adopted in the fourth quarter of 2015.