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Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) $ in Millions |  |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jul. 03, 2018 USD ($) | Jun. 29, 2018 USD ($) | Jun. 13, 2017 USD ($) | Jul. 06, 2016 guarantee | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Mar. 12, 2018 USD ($)
Payment Guarantee |  |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |  |
Number of parental guarantees | guarantee |  |  |  | 5 |  |  |
Letter of credit | ARIZONA PUBLIC SERVICE COMPANY |  |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |  |
Outstanding letters of credit |  |  |  |  | $ 0.2 |  |
Equity Lessors Sale Leaseback Letter of Credit | ARIZONA PUBLIC SERVICE COMPANY |  |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |  |
Outstanding letters of credit |  |  |  |  | 17.0 |  |
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% |  |  | 7.00% |  |  |
Four Corners | Coal Supply Agreement Arbitration |  |  |  |  |  |  |
Environmental Matters [Abstract] |  |  |  |  |  |  |
Damages sought |  |  | $ 30.0 |  |  |  |
Litigation settlement |  | $ 45.0 |  |  |  |  |
Four Corners | Coal Supply Agreement Arbitration | ARIZONA PUBLIC SERVICE COMPANY |  |  |  |  |  |  |
Environmental Matters [Abstract] |  |  |  |  |  |  |
Damages sought |  |  | $ 17.0 |  |  |  |
Litigation settlement |  | $ 34.0 |  |  |  |  |
Prepaid energy related inventory, coal |  |  |  |  |  |  | $ 24.0
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] |  |  |  |  |  |  |
Payment received for coal supply agreement |  |  |  |  |  | $ 10.0 |
Operating and maintenance cost reimbursement receivable |  |  |  |  | 10.0 | $ 20.0 |
Regional Haze Rules | Navajo Generating Station | ARIZONA PUBLIC SERVICE COMPANY |  |  |  |  |  |  |
Environmental Matters [Abstract] |  |  |  |  |  |  |
Expected environmental cost |  |  |  |  | $ 200.0 |  |
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 | Cholla and Four Corners | ARIZONA PUBLIC SERVICE COMPANY |  |  |  |  |  |  |
Environmental Matters [Abstract] |  |  |  |  |  |  |
Additional expected environment cost |  |  |  |  | 5.0 |  |
Coal Combustion Waste | Minimum | Cholla | ARIZONA PUBLIC SERVICE COMPANY |  |  |  |  |  |  |
Environmental Matters [Abstract] |  |  |  |  |  |  |
Additional expected environment cost |  |  |  |  | $ 20.0 |  |
El Paso's Interest in Four Corners | 4CA |  |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |  |
Ownership interest acquired (as a percent) |  |  |  | 7.00% | 7.00% |  |

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