Acquisitions (2014 Acquisitions - Pacer) (Narrative) (Details)	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	7 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Jul. 24, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	May. 31, 2015 USD ($)	Dec. 31, 2014 CAD	Jun. 01, 2014 USD ($)
Business Combinations [Line Items]
Amount paid under financing commitment		$ 1,098,000		$ (573,000)		$ 1,046,000	$ 1,120,000	$ 16,173,000	$ 284,000
Other current liabilities, equity method investment (in dollars)		$ 20,431,000		$ 13,890,000	$ 66,527,000	$ 17,665,000	66,527,000	26,162,000
Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties					748,300,000		748,300,000	$ 1,100,000,000
Equity Method Investee [Member]
Business Combinations [Line Items]
Other current liabilities, equity method investment (in dollars)					$ 32,400,000		$ 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%				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											CAD 71,000,000
Business combination, contingent consideration arrangements, range of outcomes, maximum unlimited							there is no maximum earn-out payment amount
Pacer [Member] | Equity Method Investments [Member]
Business Combinations [Line Items]
Number Of Equity Method Investments In Which The Company Will Cease Participation In					1		1				1
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		$ 0
Business combination, contingent consideration arrangements, range of outcomes, value, high					61,000,000		61,000,000
Pacer [Member] | Canadian Dollars [Member] | 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, assets					(49,000,000)
Pacer [Member] | Unincorporated Joint Venture [Member] | Financial Support [Member]
Business Combinations [Line Items]
Unconsolidated affiliates, outstanding commitments					$ 0		$ 0
Pacer [Member] | Unincorporated Joint Venture [Member] | Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties | CAD											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%				45.00%
Pacer [Member] | Unincorporated Joint Venture [Member] | Canadian Dollars [Member]
Business Combinations [Line Items]
Revenue from related party							$ 1,700,000
Pacer [Member] | Unincorporated Joint Venture [Member] | Canadian Dollars [Member] | Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties					$ 113,600,000		113,600,000
Pacer [Member] | Unincorporated Joint Venture [Member] | Canadian Dollars [Member] | Accounts Receivable [Member]
Business Combinations [Line Items]
Receivables, unincorporated joint venture					1,800,000		1,800,000
Pacer [Member] | Equity Method Investee [Member]
Business Combinations [Line Items]
Accounts receivable, related party					0		0
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member]
Business Combinations [Line Items]
Revenue from related party							3,100,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Financial Support [Member] | Subsequent Event [Member]
Business Combinations [Line Items]
Amount paid under financing commitment			$ 37,200,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Financial Support [Member] | Subsequent Event [Member] | Maximum [Member]
Business Combinations [Line Items]
Unconsolidated affiliates, outstanding commitments	$ 7,900,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Performance Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties					61,200,000		61,200,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Other Financial Guarantees [Member]
Business Combinations [Line Items]
Guarantees issued, related parties					3,000,000		3,000,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Guarantee of Indebtedness of Others [Member] | Current Liabilities [Member]
Business Combinations [Line Items]
Other current liabilities, equity method investment (in dollars)					$ 22,600,000		$ 22,600,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Guarantee of Indebtedness of Others [Member] | Subsequent Event [Member] | Revolving Credit Facility [Member]
Business Combinations [Line Items]
Amount paid under financing commitment	$ 20,800,000
Pacer [Member] | Equity Method Investee [Member] | Canadian Dollars [Member] | Additional Receivership Financing Commitment [Member] | Financial Support [Member] | Subsequent Event [Member] | Maximum [Member]
Business Combinations [Line Items]
Unconsolidated affiliates, outstanding commitments										$ 54,600,000