Goodwill and Other Intangible Assets (2017 Acquisitions) (Narrative) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) yr	Dec. 31, 2017 acquisition
Business Combinations [Line Items]
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, low (in dollars)	$ 23
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high (in dollars)	$ 173
Business combinations, contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited	there is no maximum payment amount
2017 Acquisitions [Member]
Business Combinations [Line Items]
Business combinations, number of acquisitions | acquisition		3
Business combinations, percentage of interests acquired	100.00%
Business combinations, acquired amortizing intangible assets, weighted average useful life (in years)		10 years
Business combinations, goodwill recognized, description	The goodwill balances for the respective acquisitions represent the estimated value of each acquired company’s geographic presence in key markets, its assembled workforce and management team industry-specific project management expertise, as well as synergies expected to be achieved from the combined operations of the acquired companies and MasTec.
Business combinations, goodwill, expected tax deductible amount (in dollars)	$ 94
Business combinations, contingent consideration, basis for amount	The contingent consideration (earn-out liability) included in the table above equals a portion of the acquired companies’ earnings before interest, taxes, depreciation and amortization (“EBITDA”) in excess of thresholds agreed upon with the sellers, if applicable. Earn-outs are generally payable annually for a period of five years, as set forth in the respective purchase agreements.
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, low (in dollars)	$ 16
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high (in dollars)	$ 161
Business combinations, contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited	there is no maximum payment amount
2017 Acquisitions [Member] | Expected Term [Member]
Business Combinations [Line Items]
Business combinations, contingent consideration, earn-out period (in years) | yr	5
2017 Acquisitions [Member] | Customer Relationships [Member]
Business Combinations [Line Items]
Business combinations, acquired amortizing intangible assets, weighted average useful life (in years)		11 years
2017 Acquisitions [Member] | Backlog [Member]
Business Combinations [Line Items]
Business combinations, acquired amortizing intangible assets, weighted average useful life (in years)		4 years
2017 Acquisitions [Member] | Other Amortizing Intangible Assets [Member]
Business Combinations [Line Items]
Business combinations, acquired amortizing intangible assets, weighted average useful life (in years)		6 years
2017 Communications Acquisition [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity	a wireline/fiber deployment construction contractor
2017 Power Generation and Industrial Acquisition [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity	a heavy civil construction services company
2017 Oil and Gas Acquisition [Member]
Business Combinations [Line Items]
Business combinations, description of acquired entity	an oil and gas pipeline equipment company