Commitments and Contingencies (Concentrations of Credit Risk) - Additional Information (Detail) - Customer Concentration Risk [Member] - Customer	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Sales Revenue, Net [Member]
Concentration Risk [Line Items]
Number of customers representing ten percent or more of concentration risk	0	0	0	0
Net Position [Member]
Concentration Risk [Line Items]
Number of customers representing ten percent or more of concentration risk			1		1
Net Position [Member] | Quanta's Electric Power Infrastructure Services Segment [Member]
Concentration Risk [Line Items]
Number of customers representing ten percent or more of concentration risk			1		1
Concentration risk percentage			18.00%		12.00%