Stock-Based Compensation and Other Employee Benefit Plans (401(k) Plan) (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
401(k) Plan Disclosure [Line Items]
Stock-based compensation plan, description	MasTec has a 401(k) plan covering all eligible employees. Subject to certain dollar limits, eligible employees may contribute up to 75% of their pre-tax annual compensation to the 401(k) plan. The Company’s matching contribution is equal to 100% of the first 3% of the employee’s salary and 50% of the next 2% of the employee’s salary, up to a maximum 4% employer match. Discretionary matching contributions, which are payable 50% in shares of MasTec common stock and 50% in cash, are paid quarterly.
401(k) plan, maximum pre-tax annual contribution per employee, percentage of annual compensation	75.00%
401(k) plan, employer matching contribution, percentage of matching contribution for first 3% of employee's salary	100.00%
401(k) plan, employer 100% matching contribution, percentage of employee's salary	3.00%
401(k) plan, employer matching contribution, percentage of matching contribution for 3% to 5% of employee's salary	50.00%
401(k) plan, employer 50% matching contribution, additional percentage of employee's salary	2.00%
401(k) plan, discretionary employer matching contribution, percentage of matching contribution payable in shares	50.00%
401(k) plan, discretionary employer matching contribution, percentage of matching contribution payable in cash	50.00%
401(k) plan, employer matching contribution (in dollars)	$ 11.9	$ 11.1	$ 10.2
Maximum [Member]
401(k) Plan Disclosure [Line Items]
401(k) plan, employer matching contribution, percentage of employee's salary	4.00%