Quarterly report pursuant to Section 13 or 15(d)

Debt Obligations - Narrative (Details)

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Debt Obligations - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
Sep. 22, 2020
Sep. 21, 2020
Sep. 30, 2019
Oct. 31, 2018
Mar. 31, 2021
Mar. 31, 2020
Jun. 30, 2020
Dec. 31, 2020
Line of Credit Facility [Line Items]                
Payments under credit facility         $ 656,818,000 $ 1,171,059,000    
Amount borrowed under the credit facility         321,703,000     $ 148,508,000
Borrowings under credit facility         $ 828,496,000 $ 1,474,452,000    
Term Loan                
Line of Credit Facility [Line Items]                
Payments under credit facility $ 1,210,000,000              
2.900% Senior Notes due 2030 | Senior Notes                
Line of Credit Facility [Line Items]                
Interest rate 2.90%       2.90%      
Debt instrument $ 1,000,000,000.00              
Proceeds from notes offering 986,700,000              
Interest payable on senior notes $ 14,500,000              
2.900% Senior Notes due 2030 | Senior Notes | Debt Instrument, Redemption, Period One                
Line of Credit Facility [Line Items]                
Redemption price, percentage 100.00%              
2.900% Senior Notes due 2030 | Senior Notes | Debt Instrument, Redemption, Period Two                
Line of Credit Facility [Line Items]                
Redemption price, percentage 100.00%              
2.900% Senior Notes due 2030 | Maximum | Senior Notes | Debt Instrument, Redemption, Period One                
Line of Credit Facility [Line Items]                
Redemption price, percentage 101.00%              
Senior Credit Facility                
Line of Credit Facility [Line Items]                
Option to increase revolving commitments under the credit agreement         $ 400,000,000.0      
Credit facility available for revolving loans or issuing new letters of credit         1,870,000,000      
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         3.5      
Acquisition threshold for leverage ratio         $ 200,000,000.0      
Maximum consolidated leverage ratio permissible under credit agreement         4.0      
Minimum consolidated interest coverage ratio         3.0      
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 Credit Facility | Minimum                
Line of Credit Facility [Line Items]                
Commitment fee   0.20%     0.275%      
Senior Credit Facility | Maximum                
Line of Credit Facility [Line Items]                
Commitment fee   0.40%     0.425%      
Senior 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 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 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 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 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 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 Credit Facility | Excess of Federal Funds Rate                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         0.50%      
Senior Credit Facility | Excess of Euro Currency Rate                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         1.00%      
Senior Credit Facility | U.S. Dollar                
Line of Credit Facility [Line Items]                
Amount borrowed under the credit facility         $ 113,100,000      
Senior Credit Facility | Canadian Dollars                
Line of Credit Facility [Line Items]                
Amount borrowed under the credit facility         33,400,000      
Senior Credit Facility | Australian Dollars                
Line of Credit Facility [Line Items]                
Amount borrowed under the credit facility         $ 175,200,000      
Senior Credit Facility | Term Loan                
Line of Credit Facility [Line Items]                
Borrowings under credit facility     $ 687,500,000 $ 600,000,000.0        
Quarterly amortization payment             $ 16,100,000  
Senior Credit Facility | Term Loan | Eurocurrency Rate | Minimum                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         1.125%      
Senior Credit Facility | Term Loan | Eurocurrency Rate | Maximum                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         1.875%      
Senior Credit Facility | Revolving Credit Facility                
Line of Credit Facility [Line Items]                
Borrowing capacity $ 2,510,000,000              
Senior Credit Facility | Revolving Loans and Letters of Credit in Alternative Currencies | U.S. Dollar                
Line of Credit Facility [Line Items]                
Borrowing capacity         $ 800,000,000.0      
Senior Credit Facility | Letters of Credit                
Line of Credit Facility [Line Items]                
Borrowing capacity         900,000,000.0      
Letters of credit and bank guarantees         319,900,000      
Senior Credit Facility | Swing Lines Loan | U.S. Dollar                
Line of Credit Facility [Line Items]                
Borrowing capacity         100,000,000.0      
Senior Credit Facility | Swing Lines Loan | Canadian Dollars                
Line of Credit Facility [Line Items]                
Borrowing capacity         50,000,000.0      
Senior Credit Facility | Swing Lines Loan | Australian Dollars                
Line of Credit Facility [Line Items]                
Borrowing capacity         50,000,000.0      
Senior Credit Facility | Letters of Credit and Bank Guarantees | Canadian Dollars                
Line of Credit Facility [Line Items]                
Letters of credit and bank guarantees         $ 100,800,000      
Senior Credit Facility | Standby Letters of Credit | Minimum                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         1.125%      
Senior Credit Facility | Standby Letters of Credit | Maximum                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         2.00%      
Senior Credit Facility | Performance Letters of Credit | Minimum                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         0.675%      
Senior Credit Facility | Performance Letters of Credit | Maximum                
Line of Credit Facility [Line Items]                
Debt instrument basis spread on variable rate         1.15%