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Fair Value Measurements Fair Value Measurements- Financial Instruments Not Carried at Fair Value (Details) $ in Millions | Sep. 30, 2018 USD ($)
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Fair Value Disclosures [Abstract] |
Stated interest rate for notes receivable | 3.90%
Note receivable, net book value | $ 65

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- Definition Note Receivable, Net Book Value + References No definition available. + Details
Name: | pnw_NoteReceivableNetBookValue
Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Stated Interest Rate for Notes Receivable + References No definition available. + Details
Name: | pnw_StatedInterestRateforNotesReceivable
Namespace Prefix: | pnw_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration