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Commitments and Contingencies - Letters of Credit (Detail) $ in Millions | Sep. 30, 2018 USD ($)
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Letters of Credit and Bank Guarantees |
Loss Contingencies [Line Items] |
Outstanding letters of credit and bank guarantees | $ 449.9

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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_CreditFacilityAxis=pwr_LettersOfCreditAndBankGuaranteesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |