Equity - Additional Information (Detail) - USD ($)		3 Months Ended			9 Months Ended
	Aug. 07, 2015	Dec. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Feb. 28, 2017	Dec. 31, 2014
Equity [Line Items]
Minimum number of shares that can be exchanged by exchangeable shareholders unless the number of remaining exchangeable shares registered in the name of the holder is less					50,000
Number of shares of Common stock received for each exchangeable share					1
Common stock, shares outstanding			156,457,392		156,457,392			210,819,790
Exchangeable shares exchanged for common stock			449,929
Payments for repurchase of common stock			$ 1,175,293,000		$ 1,529,572,000	$ 45,021,000
Income attributable to the other joint venture members			2,600,000	$ 5,400,000	10,700,000	14,000,000
Carrying value of the investments held by Quanta in variable interest entities			14,500,000		14,500,000			$ 11,100,000
Non-controlling interests			14,542,000		14,542,000			$ 11,067,000
Distributions to non-controlling interests			$ 1,500,000	$ 3,000,000	6,500,000	$ 3,500,000
2013 Repurchase Program [Member]
Equity [Line Items]
Treasury stock acquired			1,800,000
Value of treasury stock acquired, cost method			$ 52,200,000
2013 Repurchase Program [Member] | Maximum [Member]
Equity [Line Items]
Aggregate authorized amount of common stock to be repurchased			500,000,000		500,000,000
Accelerated Share Repurchase Agreement [Member]
Equity [Line Items]
Treasury stock acquired	25,700,000
Value of treasury stock acquired, cost method					600,000,000
Aggregate authorized amount of common stock to be repurchased	$ 750,000,000
Payments for repurchase of common stock	$ 750,000,000
Amount in APIC paid in ASR for shares not received			$ 150,000,000		$ 150,000,000
2015 Repurchase Plan Open Market Purchases [Member]
Equity [Line Items]
Treasury stock acquired			15,600,000
Value of treasury stock acquired, cost method			$ 373,100,000
2013 and 2015 Repurchase Program [Member]
Equity [Line Items]
Treasury stock acquired			43,100,000		55,700,000
Value of treasury stock acquired, cost method			$ 1,030,000,000		$ 1,380,000,000
Scenario Forecast [Member] | 2015 Repurchase Program [Member]
Equity [Line Items]
Treasury stock acquired		3,600,000
Value of treasury stock acquired, cost method		$ 76,800,000
Scenario Forecast [Member] | 2015 Repurchase Program [Member] | Maximum [Member]
Equity [Line Items]
Aggregate authorized amount of common stock to be repurchased							$ 1,250,000,000
Common Stock Withheld for Settlement of Employee Tax Liabilities [Member] | Treasury Stock [Member]
Equity [Line Items]
Treasury stock acquired					400,000	300,000
Value of treasury stock acquired, cost method					$ 10,100,000	$ 11,900,000
Series F Preferred Stock [Member]
Equity [Line Items]
Number of preferred Stock issued to voting trust			1		1			1
Series G Preferred Stock [Member]
Equity [Line Items]
Number of preferred Stock issued to voting trust			1		1			1
Exchangeable Shares [Member]
Equity [Line Items]
Common stock, shares outstanding			6,876,042		6,876,042			7,325,971
Series F- and Series G- Preferred Stock [Member]
Equity [Line Items]
Exchangeable stock shares outstanding			3,949,929		3,949,929