Acquisitions (2015 Acquisitions) - Additional Information (Detail) - Acquisitions 2015 [Member] $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) Entity shares
Business Acquisition [Line Items]
Cash paid or payable \| $	$ 110.6
Number of shares granted for acquired companies \| shares	461,037
Value of Quanta common stock and exchangeable shares issued \| $	$ 10.1
Contingent consideration \| $	$ 1.0
Number of business acquisitions	11
Electric Power Infrastructure Services Business [Member]
Business Acquisition [Line Items]
Number of business acquisitions	8
Electric Power Infrastructure Services Business [Member] \| United States [Member]
Business Acquisition [Line Items]
Number of business acquisitions	4
Electric Power Infrastructure Services Business [Member] \| Australia [Member]
Business Acquisition [Line Items]
Number of business acquisitions	1
Electric Power Infrastructure Services Business [Member] \| Canada [Member]
Business Acquisition [Line Items]
Number of business acquisitions	3
Oil and Gas Infrastructure Services Business [Member]
Business Acquisition [Line Items]
Number of business acquisitions	3
Oil and Gas Infrastructure Services Business [Member] \| United States [Member]
Business Acquisition [Line Items]
Number of business acquisitions	1
Oil and Gas Infrastructure Services Business [Member] \| Australia [Member]
Business Acquisition [Line Items]
Number of business acquisitions	1
Oil and Gas Infrastructure Services Business [Member] \| Canada [Member]
Business Acquisition [Line Items]
Number of business acquisitions	1

Consideration transferred or to be transferred cash and liabilities incurred except for contingent consideration.

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-Name Accounting Standards Codification
-Topic 805
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The number of businesses acquired by the entity during the period.

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