Acquisitions (2014 Acquisitions - Pacer) (Narrative) (Details)	1 Months Ended	3 Months Ended	5 Months Ended	10 Months Ended
	Mar. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Aug. 03, 2015 USD ($)	Mar. 31, 2015 USD ($)	May. 31, 2015 USD ($)	Mar. 31, 2015 CAD	Mar. 31, 2015 USD ($)	Dec. 31, 2014 CAD	Dec. 31, 2014 USD ($)	Jun. 01, 2014 USD ($)
Business Combinations [Line Items]
Other current liabilities, equity method investment							$ 43,373,000		$ 66,527,000
Prepaid expenses and other current assets							96,271,000		91,336,000
Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties							665,600,000		748,300,000
Equity Method Investee [Member]
Business Combinations [Line Items]
Other current liabilities, equity method investment							$ 1,400,000		32,400,000
Pacer [Member]
Business Combinations [Line Items]
Business combinations, effective date		Jun. 01, 2014
Business combinations, percentage of voting interests acquired						100.00%	100.00%
Business combinations, name of acquired entity		Pacer Construction Holdings Corporation and its affiliated operating companies (collectively, “Pacer”)
Business combinations, description of acquired entity		Pacer is a western Canadian civil construction services company, headquartered in Calgary, Alberta, Canada.  Pacer’s services include infrastructure construction primarily in support of oil and gas production, processing, mining and transportation.
Business combinations, goodwill recognized, description		Goodwill arising from the acquisition represents the estimated value of Pacer’s geographic presence in key high-growth Canadian markets, its assembled workforce, its management team’s industry-specific project management expertise and synergies expected to be achieved from the combined operations of Pacer and MasTec.
Business combinations, goodwill, expected tax deductible amount										$ 0
Pacer [Member] | Earn-Out Arrangements [Member]
Business Combinations [Line Items]
Business combinations, contingent consideration arrangements, basis for amount		The contingent consideration included in the table above equals 25% of the excess, if any, of Pacer’s earnings from continuing operations before interest, taxes, depreciation and amortization (“EBITDA”) above certain thresholds for a five-year period, as set forth in the purchase agreement, and is payable annually in Canadian dollars.
Business combinations, contingent consideration, percentage of excess EBITDA		25.00%
Business combinations, contingent consideration, earn-out period (in years)		5 years
Business combinations, contingent consideration, fair value measurements, significant assumptions		The fair value of the earn-out liability was estimated using an income approach and incorporates significant inputs not observable in the market. Key assumptions in the estimated valuation include the discount rate and probability-weighted EBITDA projections.
Business combination, contingent consideration arrangements, range of outcomes, value, low | CAD						CAD 0
Business combination, contingent consideration arrangements, range of outcomes, value, high | CAD						71,000,000
Business combination, contingent consideration arrangements, range of outcomes, maximum unlimited		there is no maximum earn-out payment amount
Pacer [Member] | Unincorporated Joint Venture [Member] | Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties | CAD						CAD 132,100,000		CAD 132,100,000
Pacer [Member] | Unincorporated Joint Venture [Member] | Performance Guarantees [Member] | Other [Member]
Business Combinations [Line Items]
Construction projects, percentage complete						45.00%	45.00%
Pacer [Member] | Canadian Dollars [Member]
Business Combinations [Line Items]
Business combinations, provisional information, initial accounting Incomplete, adjustment, property and equipment				$ 8,400,000
Business combinations, provisional information, initial accounting incomplete, adjustment, goodwill				47,500,000
Pacer [Member] | Canadian Dollars [Member] | Earn-Out Arrangements [Member]
Business Combinations [Line Items]
Business combination, contingent consideration arrangements, range of outcomes, value, low							$ 0
Business combination, contingent consideration arrangements, range of outcomes, value, high							56,000,000
Pacer [Member] | Canadian Dollars [Member] | Other Current Liabilities [Member]
Business Combinations [Line Items]
Business combinations, provisional information, initial accounting incomplete, adjustment, liabilities				5,600,000
Pacer [Member] | Canadian Dollars [Member] | Long-Term Deferred Tax Liabilities [Member]
Business Combinations [Line Items]
Business combinations, provisional information, initial accounting incomplete, adjustment, liabilities				1,200,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investments [Member]
Business Combinations [Line Items]
Business combinations, provisional information, initial accounting incomplete, adjustment, equity method investment				$ (49,000,000)
Pacer [Member] | Canadian Dollars [Member] | Unincorporated Joint Venture [Member]
Business Combinations [Line Items]
Revenue from related party		$ 600,000
Pacer [Member] | Canadian Dollars [Member] | Unincorporated Joint Venture [Member] | Other [Member] | Contracts Accounted for under Percentage-of-Completion [Member]
Business Combinations [Line Items]
Project losses (in dollars)		5,500,000
Pacer [Member] | Canadian Dollars [Member] | Unincorporated Joint Venture [Member] | Financial Support [Member]
Business Combinations [Line Items]
Unconsolidated affiliates, outstanding commitments							0		0
Pacer [Member] | Canadian Dollars [Member] | Unincorporated Joint Venture [Member] | Financial Support [Member] | Maximum [Member]
Business Combinations [Line Items]
Financing commitments, amounts paid		500,000
Pacer [Member] | Canadian Dollars [Member] | Unincorporated Joint Venture [Member] | Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties							104,100,000		113,600,000
Pacer [Member] | Canadian Dollars [Member] | Unincorporated Joint Venture [Member] | Accounts Receivable [Member]
Business Combinations [Line Items]
Receivables, unincorporated joint venture							2,100,000		1,800,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Financial Support [Member]
Business Combinations [Line Items]
Financing commitments, amounts paid		$ 9,300,000
Unconsolidated affiliates, outstanding commitments							0		0
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Financial Support [Member] | Pacer Equity Method Investee in Receivership [Member]
Business Combinations [Line Items]
Financing commitments, amounts paid	$ 1,600,000
Unconsolidated affiliates, outstanding commitments							7,900,000
Prepaid expenses and other current assets							1,600,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Financial Support [Member] | Pacer Equity Method Investee in Receivership [Member] | Subsequent Event [Member]
Business Combinations [Line Items]
Financing commitments, amounts paid			$ 37,200,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties							56,100,000		61,200,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Other Financial Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties							$ 2,700,000		3,000,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Guarantee of Indebtedness of Others [Member] | Other Current Liabilities [Member]
Business Combinations [Line Items]
Other current liabilities, equity method investment									$ 22,600,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Guarantee of Indebtedness of Others [Member] | Financial Support [Member] | Revolving Loans [Member]
Business Combinations [Line Items]
Financing commitments, amounts paid	$ 20,800,000
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investee [Member] | Additional Receivership Financing Commitment [Member] | Financial Support [Member] | Maximum [Member] | Pacer Equity Method Investee in Receivership [Member] | Subsequent Event [Member]
Business Combinations [Line Items]
Unconsolidated affiliates, outstanding commitments					$ 54,600,000