Acquisitions (2012 Acquisitions) (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 01, 2012	Dec. 31, 2014	Dec. 31, 2014
Bottom Line Services [Member]
Business Combinations [Line Items]
Business combinations, effective date			Dec. 01, 2012
Business combinations, name of acquired entity			Bottom Line Services, LLC (“BLS”)
Business combinations, payments in cash	$ 67.6
Business combinations, description of acquired entity			provides pipeline and facilities construction, painting and maintenance services, primarily in eastern Texas.
Bottom Line Services [Member] | Earn-Out Arrangements [Member]
Business Combinations [Line Items]
Business combinations, contingent consideration, earn-out period (in years)			5 years
Business combination, fair value of contingent consideration, liability		$ 4.6	$ 4.6
Bottom Line Services [Member] | Earn-Out Arrangements [Member] | Changes Measurement [Member]
Business Combinations [Line Items]
Business combination, contingent consideration, fair value measurement adjustment		$ (6.4)
Other December 2012 Acquisitions - Oil and Gas [Member]
Business Combinations [Line Items]
Business combinations, effective date			Dec. 01, 2012
Business combinations, description of acquired entity			a former subcontractor to MasTec’s oil and gas business, which provides self-perform clearing and trenching services for natural gas and petroleum pipeline infrastructure construction
Other December 2012 Acquisitions - Communications [Member]
Business Combinations [Line Items]
Business combinations, effective date			Dec. 01, 2012
Business combinations, description of acquired entity			a former subcontractor to MasTec’s wireless business, which provides self-perform communications tower construction, installation, maintenance and other services in support of telecommunications infrastructure construction