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Regulatory Matters - Cost Recovery Mechanism and Net Metering (Details) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 22, 2018 USD ($) | Feb. 15, 2018 USD ($) | Feb. 09, 2018 | Feb. 01, 2018 $ / kWh | Jan. 08, 2018 USD ($) | Jan. 03, 2018 | Nov. 20, 2017 USD ($) | Aug. 19, 2017 $ / kWh | Jun. 01, 2017 USD ($) | Mar. 27, 2017 USD ($) $ / kWh | Mar. 26, 2017 $ / kWh | Feb. 01, 2017 $ / kWh | Jan. 13, 2017 USD ($) | Dec. 20, 2016 $ / kWh | Jun. 01, 2016 USD ($) | Feb. 01, 2016 $ / kWh | Jan. 15, 2016 USD ($) | Jun. 01, 2011 USD ($) | Apr. 30, 2018 USD ($) | Dec. 31, 2014 penetration_feeder storage_system MW | Mar. 31, 2018 USD ($) $ / kWh | Mar. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) | Nov. 14, 2017 USD ($) | Sep. 01, 2017 USD ($) | Jan. 27, 2017 USD ($) | Jul. 01, 2016 USD ($) | Nov. 25, 2015 USD ($) | Mar. 20, 2015 project
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18,950,000 | $ 988,000 |  |  |  |  |  |  |
Amounts refunded/(charged) to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (20,002,000) | 4,172,000 |  |  |  |  |  |  |
Ballot Initiative, proposed required energy supply from renewable sources (as a percent) |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18,950,000 | 988,000 |  |  |  |  |  |  |
Amounts refunded/(charged) to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (20,002,000) | 4,172,000 |  |  |  |  |  |  |
Gross-up for revenue requirement of rate regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 377,000,000 |  |  |  |  |  |
RES 2014 | APS | Alternative to AZ Sun Program, Phase 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request to build additional utility scale solar, capacity (in MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8 |  |  |  |  |  |  |  |  |
RES 2014 | APS | Alternative to AZ Sun Program Phase 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Request to build additional utility scale solar, capacity (in MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Number of energy storage systems | storage_system |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Solar storage system, capacity (in MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Number of high solar penetration feeders | penetration_feeder |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
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 approval |  |  |  |  |  |  |  |  |  |  |  |  | $ 63,700,000 |  |  |  | $ 46,400,000 |  |  |  |  |  |  |  |  |  |  |  |
Increase in amount of adjustment representing prorated sales losses |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  | $ 17,300,000 |  |  |  | $ 7,900,000 |  |  |  |  |  |  |  |  |  |  |  |
Amount of adjustment representing prorated sales losses pending approval |  | $ 60,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross-up for revenue requirement of rate regulation |  |  |  |  | $ (119,100,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Provisional income tax expense (benefit) | $ (119,100,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Retail Rate Case Filing with Arizona Corporation Commission | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net retail base rate, increase |  |  |  |  |  |  |  |  |  | $ 94,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-fuel and non-depreciation base rate, increase |  |  |  |  |  |  |  |  |  | 87,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fuel-related base rate decrease |  |  |  |  |  |  |  |  |  | 53,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Base rate increase, changes in depreciation schedules |  |  |  |  |  |  |  |  |  | $ 61,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approximate percentage of increase in average customer bill |  |  |  |  |  |  |  |  |  | 3.28% |  |  |  |  | 5.74% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approximate percentage of increase in average residential customer bill |  |  |  |  |  | 4.54% |  |  |  | 4.54% |  |  |  |  | 7.96% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized return on common equity (as a percent) |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of debt in capital structure |  |  |  |  |  |  |  |  |  | 44.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of common equity in capital structure |  |  |  |  |  |  |  |  |  | 55.80% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  | 0.00050 | 0.00016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate matter, resource comparison proxy for exported energy (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  | 0.129 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net retail rate increase |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 165,900,000 |  |  | $ 95,500,000 |  |  |  |  |  |  |  |  |  |  |
ACC | Retail Rate Case Filing with Arizona Corporation Commission | APS | AZ Sun Program Phase 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, minimum annual renewable energy standard and tariff |  |  |  |  |  |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, maximum annual renewable energy standard and tariff |  |  |  |  |  |  |  |  |  | $ 15,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | RES | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plan term |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
ACC | RES 2017 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |
ACC | RES 2018 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 90,000,000 |  |  |  |  |  |  |  |
ACC | RES 2018 | APS | Solar Communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program term |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | DSMAC 2015 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 68,900,000 |
Number of resource savings projects | project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3
ACC | Power Supply Adjustor (PSA) | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 74,585,000 |  | 75,637,000 | 12,465,000 | 12,465,000 |  |  |  |  |  |
Deferred fuel and purchased power costs — current period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18,950,000 | 988,000 |  |  |  |  |  |  |
Amounts refunded/(charged) to customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (20,002,000) | 4,172,000 |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 74,585,000 | $ 17,625,000 | $ 75,637,000 |  |  |  |  |  |
PSA rate (in dollars per kWh) | $ / kWh |  |  |  | 0.004555 |  |  |  | 0.000555 |  |  |  | (0.001348) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward component of increase in PSA (in dollars per kWh) | $ / kWh |  |  |  | 0.002009 |  |  |  | 0.000876 |  |  |  | (0.001027) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Historical component of increase in PSA (in dollars per kWh) | $ / kWh |  |  |  | 0.002546 |  |  |  | (0.000321) |  |  |  | (0.000321) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Demand Side Management Adjustor Charge 2017 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 66,600,000 |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 62,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
ACC | Demand Side Management Adjustor Charge 2018 | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 52,600,000 | $ 52,600,000 |  |  |  |
United States Federal Energy Regulatory Commission | Open Access Transmission Tariff | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in annual wholesale transmission rates |  |  |  |  |  |  |  |  | $ 35,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost Recovery Mechanisms | ACC | Power Supply Adjustor (PSA) | APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSA rate for prior year (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.001678 |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum | ACC | RES 2018 | APS | Solar Communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required annual capital investment |  |  |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | ACC | RES 2018 | APS | Solar Communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required annual capital investment |  |  |  |  |  |  | $ 15,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change in regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Ballot Initiative, Statutory Fine Per Violation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,000 |  |  |  |  |  |  |  |  |  |

X
- Definition Amount of Adjustment Representing Prorated Sales Losses Approved + References No definition available. + Details
Name: | pnw_AmountofAdjustmentRepresentingProratedSalesLossesApproved
Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of Adjustment Representing Prorated Sales Losses Pending Approval + References No definition available. + Details
Name: | pnw_AmountofAdjustmentRepresentingProratedSalesLossesPendingApproval
Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | pnw_DeferredFuelAndPurchasedPowerRegulatoryAssetLiabilityRollForward
Namespace Prefix: | pnw_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Deferred Fuel and Purchased Power Regulatory Asset (Liability), Current + References No definition available. + Details
Name: | pnw_DeferredFuelandPurchasedPowerRegulatoryAssetLiabilityCurrent
Namespace Prefix: | pnw_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the forward component of increase in PSA. + References No definition available. + Details
Name: | pnw_ForwardComponentOfPSARate
Namespace Prefix: | pnw_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the historical component of increase in PSA. + References No definition available. + Details
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Namespace Prefix: | pnw_
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