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v3.20.2

Leases - Additional information (Details) $ in Millions | Sep. 30, 2020 USD ($) Lease | Jun. 01, 2020 Lease
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Leases [Abstract] |  |
Number of lease agreements, lease and sell back | 3 |
Number of lease agreements |  | 2
Lease not yet commenced | $ | $ 258 |

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- Definition Lease Not yet Commenced, Liability, Lease and Nonlease Payments + References No definition available. + Details
Name: | pnw_LeaseNotyetCommencedLiabilityLeaseandNonleasePayments
Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Number Of Lease Agreements + References No definition available. + Details
Name: | pnw_NumberOfLeaseAgreements
Namespace Prefix: | pnw_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Number Of Lease Agreements, Lease And Sell Back + References No definition available. + Details
Name: | pnw_NumberOfLeaseAgreementsLeaseAndSellBack
Namespace Prefix: | pnw_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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