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Regulatory Matters - Cost Recovery Mechanism and Net Metering (Details) Customer in Thousands |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 14, 2020 USD ($) | Feb. 01, 2020 USD ($) $ / kWh | Nov. 14, 2019 USD ($) Customer | Oct. 31, 2019 USD ($) | Oct. 29, 2019 USD ($) | Jun. 01, 2019 USD ($) | Apr. 10, 2019 | Feb. 15, 2019 USD ($) | Feb. 01, 2019 $ / kWh | Aug. 13, 2018 USD ($) | Jun. 01, 2018 USD ($) | May 01, 2018 $ / kWh | Feb. 15, 2018 USD ($) | Feb. 01, 2018 $ / kWh | Jan. 08, 2018 USD ($) | Nov. 20, 2017 USD ($) | Dec. 20, 2016 $ / kWh | Aug. 31, 2016 | Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2017 $ / kWh | Dec. 31, 2012 $ / kWh | May 05, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jul. 01, 2019 USD ($) | Mar. 15, 2019 agreement | Dec. 31, 2018 USD ($) | Jun. 29, 2018 USD ($) | Nov. 14, 2017 USD ($) | Sep. 01, 2017 USD ($)
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14,657,000 | $ 25,209,000 |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,785,000 | (16,709,000) |  |  |  |  |  |  |  |  |  |  |
Amounts charged to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,808,000 | (12,872,000) |  |  |  |  |  |  |  |  |  |  |
Rate plan comparison tool, number of customers | Customer |  |  | 13 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate plan comparison tool, inconvenience payment |  |  | $ 25 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,770,000 | 34,602,000 |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,785,000 | (16,709,000) |  |  |  |  |  |  |  |  |  |  |
Amounts charged to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,808,000 | (12,872,000) |  |  |  |  |  |  |  |  |  |  |
Lost Fixed Cost Recovery Mechanisms | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed costs recoverable per residential power lost (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.031 |  |  |  |  |  |  |  |
Fixed costs recoverable per non-residential power lost (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.023 |  |  |  |  |  |  |  |
Fixed cost recoverable per power lost (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.025 |  |  |  |  |  |  |  |  |
Percentage of retail revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |  |  |  |  |  |
Amount of adjustment representing prorated sales losses pending approval | $ 26,600,000 |  |  |  |  |  |  | $ 36,200,000 |  |  |  |  | $ 60,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in amount of adjustment representing prorated sales losses | $ (9,600,000) |  |  |  |  |  |  | $ (24,500,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program term |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross-up for revenue requirement of rate regulation |  |  |  | $ (184,000,000) |  |  |  |  |  | $ 86,500,000 |  |  |  |  | $ 119,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred taxes amortization, period |  |  |  |  |  |  | 28 years 6 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, one-time bill credit |  |  |  |  | $ 64,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, one-time bill credit, additional benefit |  |  |  |  | $ 39,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | RES | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plan term |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |
ACC | RES 2018 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 86,300,000 |  |  | $ 89,900,000 |  |
ACC | RES 2018 | APS | Solar Communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program term |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Demand Side Management Adjustor Charge 2018 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 52,600,000 | $ 52,600,000
ACC | Demand Side Management Adjustor Charge 2019 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34,100,000 |  |  |
ACC | Demand Side Management Adjustor Charge 2020 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 51,900,000 |  |  |  |  |  |
ACC | Power Supply Adjustor (PSA) | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 70,137,000 | 37,164,000 | $ 70,137,000 |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,785,000 | (16,709,000) |  |  |  |  |  |  |  |  |  |  |
Amounts charged to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,808,000 | (12,872,000) |  |  |  |  |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 77,730,000 | $ 7,583,000 |  |  |  |  |  |  |  |  |  |  |
PSA rate (in dollars per kWh) | $ / kWh |  | (0.000456) |  |  |  |  |  |  | 0.001658 |  |  |  |  | 0.004555 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSA rate for prior year (in dollars per kWh) | $ / kWh |  | (0.002086) |  |  |  |  |  |  | 0.000536 |  |  |  |  | 0.002009 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward component of increase in PSA (in dollars per kWh) | $ / kWh |  | 0.001630 |  |  |  |  |  |  | 0.001122 |  |  |  |  | 0.002546 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum increase (decrease) in PSA rate | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.004 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fuel and purchased power costs, excess annual limit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 16,400,000 |  |  |  |  |  |  |  |  |  |  |  |
ACC | Net Metering | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of service, resource comparison proxy method, maximum annual percentage decrease |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of service for interconnected DG system customers, grandfathered period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of service for new customers, guaranteed export price period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
First-year export energy price (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.129 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Second-year export energy price (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  | 0.116 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
United States Federal Energy Regulatory Commission | Environmental Improvement Surcharge [Member] | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual wholesale transmission rates |  | $ 8,750,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
United States Federal Energy Regulatory Commission | Open Access Transmission Tariff | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual wholesale transmission rates |  |  |  |  |  | $ 4,900,000 |  |  |  |  | $ (22,700,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost Recovery Mechanisms | ACC | Power Supply Adjustor (PSA) | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Historical component of increase in PSA (in dollars per kWh) | $ / kWh |  | (0.002115) |  |  |  |  |  |  | (0.002897) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost Recovery, Number Of Agreements | agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |
Forecast | United States Federal Energy Regulatory Commission | Environmental Improvement Surcharge [Member] | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate Matters, Increase (Decrease) in Cost Recovery, Excess Of Annual Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (2,000,000.0) |  |  |  |  |  |  |  |  |  |
Minimum | ACC | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Results |  |  |  | $ (69,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum | ACC | RES 2018 | APS | Solar Communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required annual capital investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | ACC | RES 2018 | APS | Solar Communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required annual capital investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 15,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Demand side management funds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 36,000,000 |  |  |  |  |  |  |
Damage from Fire, Explosion or Other Hazard | Minimum | Forecast | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000 |  |  |  |  |  |  |  |  |  |
Damage from Fire, Explosion or Other Hazard | Maximum | Forecast | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 30,000,000 |  |  |  |  |  |  |  |  |  |

X
- Definition Amount of Adjustment Representing Prorated Sales Losses Pending Approval + References No definition available. + Details
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- Definition Cost Recovery, Number Of Agreements + References No definition available. + Details
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Namespace Prefix: | pnw_
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Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
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Namespace Prefix: | pnw_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Deferred Fuel and Purchased Power Regulatory Asset (Liability), Current + References No definition available. + Details
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Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
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X
- Definition Forward Component of PSA Rate1 + References No definition available. + Details
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Namespace Prefix: | pnw_
Data Type: | srt-types:perUnitItemType
Balance Type: | na
Period Type: | duration

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- Definition Fuel And Purchased Power Costs, Excess Annual Limit + References No definition available. + Details
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Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
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