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Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) - USD ($) $ in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Jul. 03, 2018 | Jul. 06, 2016 | Dec. 31, 2019
Financial Assurances |  |  |
Equity contribution guarantees |  |  | $ 40.0
Letter of credit | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Financial Assurances |  |  |
Outstanding letters of credit |  |  | 1.7
Four Corners | NTEC |  |  |
Environmental Matters [Abstract] |  |  |
Option to purchase, ownership interest (as a percent) | 7.00% | 7.00% |
Payment received for coal supply agreement | $ 70.0 |  |
Four Corners | 4CA |  |  |
Environmental Matters [Abstract] |  |  |
Percentage share cost of control |  | 7.00% |
Four Corners | Coal Supply Agreement Arbitration | NTEC |  |  |
Environmental Matters [Abstract] |  |  |
Option to purchase, ownership interest (as a percent) |  | 7.00% |
Four Corners | Coal Supply Agreement Arbitration | 4CA |  |  |
Environmental Matters [Abstract] |  |  |
Asset purchase agreement |  |  | $ 10.0
Regional Haze Rules | Four Corners Units 4 and 5 | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Percentage share cost of control |  |  | 63.00%
Expected environmental cost |  |  | $ 400.0
Regional Haze Rules | Four Corners Units 4 and 5 | Four Corners | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional expected environment cost |  |  | $ 45.0
Regional Haze Rules | Four Corners Units 4 and 5 | Natural Gas Tolling Letter of Credit | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional percentage share of cost of control |  |  | 7.00%
Coal Combustion Waste | Four Corners | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional expected environment cost |  |  | $ 22.0
Coal Combustion Waste | Navajo Generating Station | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional expected environment cost |  |  | 1.0
Coal Combustion Waste | Minimum | Cholla | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional expected environment cost |  |  | 15.0
Coal Combustion Waste | Minimum | Cholla and Four Corners | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional expected environment cost |  |  | 10.0
Coal Combustion Waste | Maximum | Cholla and Four Corners | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Environmental Matters [Abstract] |  |  |
Additional expected environment cost |  |  | 15.0
Surety Bonds Expiring in 2020 | ARIZONA PUBLIC SERVICE COMPANY |  |  |
Financial Assurances |  |  |
Surety bonds expiring, amount |  |  | $ 14.0

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