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Regulatory Matters - Narrative (Details) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 12 Months Ended |  |  |  |  |  |  |
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Feb. 22, 2018 USD ($) | Feb. 15, 2018 USD ($) | Feb. 09, 2018 | Feb. 01, 2018 $ / kWh | Jan. 08, 2018 USD ($) | Nov. 20, 2017 USD ($) | Aug. 19, 2017 $ / kWh | Jun. 01, 2017 USD ($) | Feb. 01, 2017 $ / kWh | Jan. 13, 2017 USD ($) | Dec. 20, 2016 $ / kWh | Jun. 01, 2016 USD ($) | Feb. 01, 2016 $ / kWh | Jan. 15, 2016 USD ($) | Jan. 01, 2016 USD ($) | Feb. 01, 2015 $ / kWh | Nov. 04, 2014 | Jun. 01, 2011 USD ($) | Sep. 30, 2016 | Dec. 31, 2014 penetration_feeder storage_system MW | Apr. 30, 2014 workshop | Dec. 31, 2017 USD ($) $ / kWh | Dec. 31, 2012 $ / kWh | Nov. 14, 2017 USD ($) | Sep. 01, 2017 USD ($) | Jun. 30, 2017 USD ($) | Jan. 27, 2017 USD ($) | Jul. 01, 2016 USD ($) | Nov. 25, 2015 USD ($) | Mar. 20, 2015 project
APS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate decrease for tax act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (377,000,000) |  |  |  |  |  |  |  |
APS | Lost Fixed Cost Recovery Mechanism |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 costs recoverable per power lost (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.025 |  |  |  |  |  |  |  |
Rate matter cap percentage of retail revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |  |
Amount of adjustment approved representing prorated sales losses |  |  |  |  |  |  |  |  |  | $ 63,700,000 |  |  |  | $ 46,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in amount of adjustment representing prorated sales losses |  |  |  |  |  |  |  |  |  | $ 17,300,000 |  |  |  | $ 7,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS | ACC | Retail Rate Case Filing with Arizona Corporation Commission |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net retail rate increase |  |  |  |  |  |  |  |  |  |  |  | $ 165,900,000 |  |  |  |  |  | $ 95,500,000 |  |  |  |  |  |  |  |  |  |  |  |
Reduced system benefits charge, amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS | ACC | Arizona Renewable Energy Standard and Tariff |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plan term |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
APS | ACC | Arizona Renewable Energy Standard and Tariff 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |
APS | ACC | Arizona Renewable Energy Standard and Tariff 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 90,000,000 |  |  |  |
APS | ACC | Modernization and Expansion of the Renewal Energy Standard |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed renewal energy standard, percent of retail sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30.00% |  |  |  |  |  |  |  |  |  |  |
Current renewal energy standard, percent of retail sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |  |  |  |  |  |  |  |  |
APS | ACC | 2015 DSMAC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 68,900,000 |
Rate matter number of resource savings projects | project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3
APS | ACC | 2017 DSMAC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of approved budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 66,600,000 |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  | 62,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS | ACC | Demand Side Management Adjustor Charge 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of proposed budget |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 52,600,000 | $ 52,600,000 |  |  |  |  |
APS | ACC | Electric Energy Efficiency Standard |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, cost effective energy efficiency programs, number of workshops | workshop |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |
Public utilities, cost effective efficiency programs, number of days to convene a workshop |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 120 days |  |  |  |  |  |  |  |  |  |  |  |  |
APS | ACC | Power Supply Adjustor (PSA) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSA rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  | 0.000555 |  | (0.001348) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward component of PSA rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  | 0.000876 |  | (0.001027) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Historical component of PSA rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  | (0.000321) |  | (0.000321) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS | ACC | Net Metering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guaranteed export price period |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement agreement, energy price for exported energy (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  | 0.129 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
APS | FERC | Transmission rates, transmission cost adjustor and other transmission matters |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in annual wholesale transmission rates |  |  |  |  |  |  |  | $ 35,100,000 |  |  |  | $ 24,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost Recovery Mechanisms | APS | ACC | Power Supply Adjustor (PSA) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum increase (decrease) in PSA rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.004 |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSA Rate in Prior Years | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  | 0.001678 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ballot initiative, proposed required energy supply to be obtained from renewable sources (as a percent) |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | APS | Lost Fixed Cost Recovery Mechanism |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in amount of adjustment representing prorated sales losses |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of adjustment approved representing prorated sales losses pending approval |  | $ 60,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | APS | ACC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate decrease for tax act |  |  |  |  | $ 119,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate decrease for tax act | $ 119,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | APS | ACC | Power Supply Adjustor (PSA) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSA rate (in dollars per kWh) | $ / kWh |  |  |  | 0.004555 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward component of PSA rate (in dollars per kWh) | $ / kWh |  |  |  | 0.002009 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Historical component of PSA rate (in dollars per kWh) | $ / kWh |  |  |  | 0.002546 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Alternative to AZ Sun Program, Phase 1 | APS | Arizona Renewable Energy Standard and Tariff 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate matter additional capacity from AZ Sun projects | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8 |  |  |  |  |  |  |  |  |  |
Solar Partner Program Phase 2 | APS | Arizona Renewable Energy Standard and Tariff 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate matter additional capacity from AZ Sun projects | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |
Solar storage system, capacity (in MW) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |
Number of energy storage systems | storage_system |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |
Number of high solar penetration feeders | penetration_feeder |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |
Solar Communities | APS | ACC | Arizona Renewable Energy Standard and Tariff 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program term |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum | Solar Communities | APS | ACC | Arizona Renewable Energy Standard and Tariff 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required annual capital investment |  |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Solar Communities | APS | ACC | Arizona Renewable Energy Standard and Tariff 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required annual capital investment |  |  |  |  |  | $ 15,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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
- 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
Name: | pnw_HistoricalComponentOfPSARate
Namespace Prefix: | pnw_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Maximum Increase (Decrease) in PSA Rate + References No definition available. + Details
Name: | pnw_MaximumIncreaseDecreaseinPSARate
Namespace Prefix: | pnw_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the PSA rate (power supply adjustor) which provides for the adjustment of retail rates to reflect variations in retail fuel and purchased power costs. + References No definition available. + Details
Name: | pnw_PSARate
Namespace Prefix: | pnw_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the PSA rate prior for the prior years (power supply adjustor) which provides for the adjustment of retail rates to reflect variations in retail fuel and purchased power costs. + References No definition available. + Details
Name: | pnw_PSARateInPriorYears
Namespace Prefix: | pnw_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

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- Definition Public Utilities, Ballot Initiative, Proposed Required Energy Supply From Renewable Sources, Percent + References No definition available. + Details
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