Commitments And Contingencies (Narrative) (Detail) In Millions, unless otherwise specified	9 Months Ended					9 Months Ended	3 Months Ended	9 Months Ended								95845 Months Ended	95854 Months Ended												9 Months Ended			9 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Oct. 31, 2012 Aon Risk Services Inc [Member] Scenario, Forecast [Member] Insurance Settlement [Member] USD ($)	Sep. 30, 2012 Workers' Compensation Policy [Member] USD ($)	Sep. 30, 2012 General Liability Policy [Member] USD ($)	Sep. 30, 2012 Automobile Liability Policy [Member] USD ($)	Sep. 30, 2012 Umbrella Policy [Member] USD ($)	Sep. 30, 2012 Pending Litigation [Member] Sintel [Member] USD ($)	Sep. 30, 2012 Pending Litigation [Member] Sintel [Member] USD ($)	Sep. 30, 2012 Pending Litigation [Member] Sintel [Member] EUR (€)	Sep. 30, 2012 Pending Litigation [Member] City Of Marathon [Member]	Sep. 30, 2012 Letter of Credit [Member] USD ($)	Sep. 30, 2012 Guarantee Obligations [Member] Letter of Credit [Member] USD ($)	Dec. 31, 2011 Guarantee Obligations [Member] Letter of Credit [Member] USD ($)	Sep. 30, 2012 Performance Guarantee [Member] USD ($)	Dec. 31, 2011 Performance Guarantee [Member] USD ($)	Dec. 31, 9999 Performance Guarantee [Member] Scenario, Forecast [Member] USD ($)	Dec. 31, 9999 Performance Guarantee [Member] Scenario, Forecast [Member] USD ($)	Sep. 30, 2012 Insurance Claims [Member] USD ($)	Dec. 31, 2011 Insurance Claims [Member] USD ($)	Sep. 30, 2012 Insurance Claims [Member] Workers Compensation, General And Automobile Policies [Member] USD ($)	Dec. 31, 2011 Insurance Claims [Member] Workers Compensation, General And Automobile Policies [Member] USD ($)	Sep. 30, 2012 Insurance Claims [Member] Employee Group Health Claims Policy [Member] USD ($)	Dec. 31, 2011 Insurance Claims [Member] Employee Group Health Claims Policy [Member] USD ($)	Sep. 30, 2012 Insurance Claims [Member] Employee Group Health Claims Policy [Member] Per Employee [Member] USD ($)	Sep. 30, 2012 Insurance Claims [Member] Standby Letters of Credit [Member] USD ($)	Dec. 31, 2011 Insurance Claims [Member] Standby Letters of Credit [Member] USD ($)	Sep. 30, 2012 Insurance Claims [Member] Surety Bond [Member] USD ($)	Dec. 31, 2011 Insurance Claims [Member] Surety Bond [Member] USD ($)	Sep. 30, 2012 Multiemployer Plans, Pension [Member]	Sep. 30, 2012 Central States Southeast And Southwest Areas Pension Fund [Member] Multiemployer Plans, Pension [Member] USD ($)	Sep. 30, 2012 Minimum [Member] Aon Risk Services Inc [Member] Positive Outcome of Litigation [Member] USD ($)	Sep. 30, 2012 Minimum [Member] Pending Litigation [Member] City Of Marathon [Member] USD ($)	Sep. 30, 2012 Segment, Continuing Operations [Member] USD ($)	Sep. 30, 2011 Segment, Continuing Operations [Member] USD ($)	Sep. 30, 2012 Segment, Continuing Operations [Member] USD ($)	Sep. 30, 2011 Segment, Continuing Operations [Member] USD ($)
Commitment And Contingencies [Line Items]
Claims sought																															$ 5
Former gain contingency, recognized in period		3.5
Legal proceeding, plaintiff								The labor union representing the workers of Sistemas e Instalaciones de Telecomunicacion S.A. (“Sintel”)	The labor union representing the workers of Sistemas e Instalaciones de Telecomunicacion S.A. (“Sintel”)	the Company
Damages sought								386	300																							6
Pending or threatened litigation, estimated loss							10
Operating leases, rent expense																																	69.4	44.3	168.2	127.2
Letters of credit, outstanding amount											99.4	99.4	90.0												51.2	51.4
Outstanding bonds, amount														987.1	905.7												9.0	7.1
Estimated cost to complete bonded projects																334.8	330.0
Per claim deductible, insurance policies			1	2	2
Maximum coverage, per claim and aggregate						100
Self insurance reserve																				47.4	39.1	1.7	1.4
Self insurance reserve, noncurrent																				30.1	22.3
Maximum annual loss																								0.4
Cash collateral held by insurance carriers																		2.0	2.0
Underfunded multi-employer pension plans, funding requirements and penalties, description																													The Pension Protection Act requires that underfunded pension plans improve their funding ratios within prescribed intervals based on the level of their underfunding. In addition, if a multi-employer defined benefit plan fails to satisfy certain minimum funding requirements, the Internal Revenue Service may impose on the employers contributing to such plan a nondeductible excise tax of 5% on the amount of the accumulated funding deficiency.
Multi-employer pension plan withdrawal liability																														$ 6.4
Multi-employer pension plan withdrawal obligation, description																														On November 15, 2011, the Company, along with other members of the Pipe Line Contractors Association (“PLCA”), voluntarily withdrew from the Central States Southeast and Southwest Areas Pension Fund (“Central States”), a defined benefit multi-employer pension plan. In connection with this withdrawal, the Company recorded a $6.4 million withdrawal liability based on an estimate provided by the plan administrator of such liability as of the date of withdrawal. The Company withdrew from the Central States Plan in order to mitigate its liability in connection with the plan, which is in critical status; however, the plan has asserted that the PLCA members did not effectively withdraw on November 15, 2011. Although the Company believes that it legally and effectively withdrew from the plan on November 15, 2011, if the plan were to prevail in its assertion that the Company in fact withdrew after that date, then the amount of the Company’s withdrawal liability would increase. In addition, if this plan were to undergo a mass withdrawal, as defined by the Pension Benefit Guaranty Corporation, within the three year period commencing with the beginning of the calendar year during which the Company withdrew from the plan, there could be additional liability. The Company currently does not have plans to withdraw from any other multi-employer pension plan.
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.