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Regulatory Matters - Retail Rate Case Filing (Details) | Aug. 02, 2021 USD ($) | Nov. 06, 2020 USD ($) | Oct. 02, 2020 USD ($) | Oct. 31, 2019 USD ($) $ / kWh GW | Jun. 30, 2019 USD ($) | Aug. 13, 2018 USD ($) | Jan. 08, 2018 USD ($) | Mar. 27, 2017 USD ($) $ / kWh | Dec. 31, 2020 USD ($) | Dec. 04, 2020 USD ($)
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ACC |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Revenue increase (decrease) |  | $ 169,000,000 | $ 89,700,000 |  |  |  |  |  |  | $ 59,800,000
Average annual customer bill increase (decrease), percent |  | 5.14% | 2.70% |  |  |  |  |  |  | 1.82%
Recommended return on equity, percentage |  | 10.00% | 9.40% |  |  |  |  |  |  |
Alternative, percentage |  |  | 0.30% |  |  |  |  |  |  |
Increment of fair value rate, percentage |  | 0.80% | 0.00% |  |  |  |  |  |  |
Residential Utility Consumer Office |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Revenue increase (decrease) |  |  | $ (20,800,000) |  |  |  |  |  |  | $ (50,100,000)
Average annual customer bill increase (decrease), percent |  |  | (0.63%) |  |  |  |  |  |  | (1.52%)
Recommended return on equity, percentage |  |  | 8.74% |  |  |  |  |  |  |
Increment of fair value rate, percentage |  |  | 0.00% |  |  |  |  |  |  |
ACC | APS |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Proposed annual revenue increase |  |  |  | $ 184,000,000 |  | $ (86,500,000) | $ (119,100,000) |  |  |
Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Base rate decrease, elimination of tax expense adjustment mechanism |  |  |  | $ 115,000,000 |  |  |  |  |  |
Approximate percentage of increase in average customer bill |  |  |  | 5.60% |  |  |  | 3.28% |  |
Approximate percentage of increase in average residential customer bill |  |  |  | 5.40% |  |  |  | 4.54% |  |
Rate matter, cost base rate |  |  |  |  | $ 8,870,000,000 |  |  |  |  |
Base fuel rate (in dollars per kWh) | $ / kWh |  |  |  | 0.030168 |  |  |  |  |  |
Funding limited income crisis bill program |  |  |  | $ 1,250,000 |  |  |  |  |  |
Commercial customers, market pricing, threshold | GW |  |  |  | 0.02 |  |  |  |  |  |
Expenses from recovery of deferral and rate base effects |  |  | $ 110,000,000 |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  | $ 61,000,000.0 |  |
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, resource comparison proxy for exported energy (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  | 0.129 |  |
Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS | Subsequent Event |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Revenue increase (decrease) | $ (111,000,000) |  |  |  |  |  |  |  |  |
Recommended return on equity, percentage | 9.16% |  |  |  |  |  |  |  |  |
Increment of fair value rate, percentage | 0.15% |  |  |  |  |  |  |  |  |
Reduction on equity percentage | 0.10% |  |  |  |  |  |  |  |  |
Effective fair value percentage | 0.05% |  |  |  |  |  |  |  |  |
AZ Sun Program Phase 2 | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Public utilities, minimum annual renewable energy standard and tariff |  |  |  |  |  |  |  | $ 10,000,000 |  |
Public utilities, maximum annual renewable energy standard and tariff |  |  |  |  |  |  |  | $ 15,000,000 |  |
Coal Community Transition Plan | ACC |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by customers |  | $ 100,000,000 |  |  |  |  |  |  |  |
Amount funded by customers, term |  | 10 years |  |  |  |  |  |  |  |
Amount funded by shareholders |  | $ 25,000,000 |  |  |  |  |  |  | $ 25,000,000 |
Coal Community Transition Plan | ACC | Navajo Nation, Economic Development Organization |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by shareholders |  | $ 1,250,000 |  |  |  |  |  |  |  |
Amount funded by shareholders, term |  | 5 years |  |  |  |  |  |  |  |
Coal Community Transition Plan | ACC | Navajo Nation, Electrification Projects |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by customers |  | $ 10,000,000 |  |  |  |  |  |  |  |
Amount funded by shareholders |  | 10,000,000 |  |  |  |  |  |  |  |
Coal Community Transition Plan | ACC | Navajo Nation, Transmission Revenue Sharing |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by shareholders |  | 2,500,000 |  |  |  |  |  |  |  |
Coal Community Transition Plan | ACC | Navajo County Communities, Cholla Power Plant Closure |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by customers |  | $ 12,000,000 |  |  |  |  |  |  |  |
Amount funded by customers, term |  | 5 years |  |  |  |  |  |  |  |
Coal Community Transition Plan | ACC | Navajo Nation, Generation Station |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by customers |  | $ 3,700,000 |  |  |  |  |  |  |  |
Coal Community Transition Plan | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS | Navajo Nation, Economic Development Organization | Subsequent Event |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Disallowance of annual amortization percentage | 15.00% |  |  |  |  |  |  |  |  |
Amount funded by customers | $ 50,000,000 |  |  |  |  |  |  |  |  |
Amount funded by customers, term | 10 years |  |  |  |  |  |  |  |  |
Coal Community Transition Plan | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS | Navajo County Communities, Cholla Power Plant Closure | Subsequent Event |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by shareholders | $ 5,000,000 |  |  |  |  |  |  |  |  |
Amount funded by shareholders, term | 5 years |  |  |  |  |  |  |  |  |
Coal Community Transition Plan | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS | Navajo Nation, Hopi Tribe | Subsequent Event |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Amount funded by shareholders | $ 1,675,000 |  |  |  |  |  |  |  |  |
Minimum | ACC | APS |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Annual increase in retail base rates |  |  |  | $ 69,000,000 |  |  |  |  |  |
Minimum | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  | 0.00016 |  |
Maximum | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh |  |  |  |  |  |  |  | 0.00050 |  |

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