Debt Obligations - Narrative (Details)		1 Months Ended		3 Months Ended
	Sep. 12, 2019 USD ($)	Sep. 30, 2019 USD ($)	Oct. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Borrowings under credit facility				$ 1,474,452,000		$ 1,647,074,000
Amount borrowed under the credit facility				1,635,366,000	$ 1,346,290,000
Senior Secured Credit Facility
Line of Credit Facility [Line Items]
Option to increase revolving commitments under the credit agreement	$ 400,000,000.0
Maximum consolidated leverage ratio permissible under credit agreement	2.5
Amount borrowed under the credit facility				1,640,000,000
Credit facility available for revolving loans or issuing new letters of credit				1,350,000,000
Reduction in Quanta's funded indebtedness reduced by cash and cash equivalents in excess of this amount				$ 25,000,000.0
Maximum consolidated leverage ratio				3.0
Acquisition threshold for leverage ratio				$ 200,000,000.0
Maximum leverage ratio acquisition completed in current and two subsequent quarters				3.5
Minimum consolidated interest coverage ratio				3.0
Percentage of capital stock of direct foreign subsidiaries of wholly owned U.S. subsidiaries to secure credit agreement				65.00%
Amount of availability under the credit agreement and/or cash and cash equivalents on hand that must be present to allow for cash payments of dividends and stock repurchases				$ 100,000,000.0
Cross default provisions with debt instruments exceeding this amount				$ 150,000,000.0
Senior Secured Credit Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee				0.20%
Senior Secured Credit Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee				0.40%
Senior Secured Credit Facility | Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.125%
Senior Secured Credit Facility | Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				2.00%
Senior Secured Credit Facility | Excess of Base Rate Domestic Borrowings Only | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				0.125%
Senior Secured Credit Facility | Excess of Base Rate Domestic Borrowings Only | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.00%
Senior Secured Credit Facility | Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.125%
Senior Secured Credit Facility | Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				2.00%
Senior Secured Credit Facility | Excess of Federal Funds Rate
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				0.50%
Senior Secured Credit Facility | Excess of Euro Currency Rate
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.00%
Senior Secured Credit Facility | U.S. Dollar
Line of Credit Facility [Line Items]
Amount borrowed under the credit facility				$ 1,480,000,000
Senior Secured Credit Facility | Canadian Dollars
Line of Credit Facility [Line Items]
Amount borrowed under the credit facility				128,700,000
Senior Secured Credit Facility | Australian Dollars
Line of Credit Facility [Line Items]
Amount borrowed under the credit facility				30,700,000
Senior Secured Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Borrowing capacity	$ 2,140,000,000
Amount borrowed under the credit facility				410,100,000
Senior Secured Credit Facility | Term Loan
Line of Credit Facility [Line Items]
Borrowing capacity	$ 1,290,000,000
Borrowings under credit facility		$ 687,500,000	$ 600,000,000.0
Amount borrowed under the credit facility				1,230,000,000
Quarterly amortization payment				$ 7,500,000	$ 16,100,000
Senior Secured Credit Facility | Term Loan | Eurocurrency Rate | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.125%
Senior Secured Credit Facility | Term Loan | Eurocurrency Rate | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.875%
Senior Secured Credit Facility | Revolving Loans and Letters of Credit in Alternative Currencies | U.S. Dollar
Line of Credit Facility [Line Items]
Borrowing capacity				$ 600,000,000.0
Senior Secured Credit Facility | Swing Lines Loan | U.S. Dollar
Line of Credit Facility [Line Items]
Borrowing capacity				100,000,000.0
Senior Secured Credit Facility | Swing Lines Loan | Canadian Dollars
Line of Credit Facility [Line Items]
Borrowing capacity				50,000,000.0
Senior Secured Credit Facility | Swing Lines Loan | Australian Dollars
Line of Credit Facility [Line Items]
Borrowing capacity				50,000,000.0
Senior Secured Credit Facility | Letters of Credit and Bank Guarantees | U.S. Dollar
Line of Credit Facility [Line Items]
Letters of credit and bank guarantees				252,300,000
Senior Secured Credit Facility | Letters of Credit and Bank Guarantees | Primarily Canadian and Australian Dollars
Line of Credit Facility [Line Items]
Letters of credit and bank guarantees				121,600,000
Senior Secured Credit Facility | Letters of Credit
Line of Credit Facility [Line Items]
Letters of credit and bank guarantees				$ 373,900,000
Senior Secured Credit Facility | Standby Letters of Credit | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.125%
Senior Secured Credit Facility | Standby Letters of Credit | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				2.00%
Senior Secured Credit Facility | Performance Letters of Credit | Minimum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				0.675%
Senior Secured Credit Facility | Performance Letters of Credit | Maximum
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate				1.15%