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Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) $ in Millions |  |  |  |  |  | 6 Months Ended
--- | --- | --- | --- | --- | --- | ---
Jul. 06, 2016 guarantee | Jun. 30, 2016 USD ($) Letter_of_credit | Jun. 24, 2016 | Mar. 16, 2016 USD ($) | May 23, 2013 USD ($) | Jun. 30, 2016 USD ($) Letter_of_credit
Environmental Matters |  |  |  |  |  |
Clean power plan, optional extension period |  |  |  |  |  | 2 years
Four Corners | New Mexico Tax Matter |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Coal severance surtax, penalty, and interest |  |  |  |  | $ 30.0 |
Litigation settlement awarded (against), amount |  |  |  | $ (1.0) |  |
Arizona Public Service Company | Letter of Credit Expiring in 2016 and 2017 |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |
Outstanding letters of credit |  | $ 79.0 |  |  |  | $ 79.0
Arizona Public Service Company | Letters of Credit Expiring in 2017 |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |
Number of letters of credit expiring | Letter_of_credit |  | 150,000,000 |  |  |  | 150,000,000
Arizona Public Service Company | Four Corners | New Mexico Tax Matter |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Share of the assessment |  |  |  |  | 12.0 |
Partial payment of assessment |  |  |  |  | $ 0.8 |
Litigation settlement awarded (against), amount |  |  |  | $ (0.8) |  |
4C Acquisition, LLC | Four Corners Units 4 and 5 |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Percentage of share of cost of control |  |  |  |  |  | 7.00%
Regional Haze Rules | Arizona Public Service Company | Four Corners Units 4 and 5 |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Percentage of share of cost of control |  |  |  |  |  | 63.00%
Expected environmental cost |  |  |  |  |  | $ 400.0
Regional Haze Rules | Arizona Public Service Company | Natural gas tolling contract obligations | Four Corners Units 4 and 5 |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Additional percentage share of cost of control |  |  |  |  |  | 7.00%
Regional Haze Rules | Arizona Public Service Company | Four Corners | Four Corners Units 4 and 5 |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | $ 45.0
Regional Haze Rules | Arizona Public Service Company | Navajo Plant |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Expected environmental cost |  |  |  |  |  | 200.0
Regional Haze Rules | Arizona Public Service Company | Cholla |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Expected environmental cost |  |  |  |  |  | 100.0
Proposal comment period |  | 45 days |  |  |  |
Mercury and air toxic standards (MATS) | Arizona Public Service Company | Navajo Plant |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Expected environmental cost |  |  |  |  |  | 1.0
Mercury and air toxic standards (MATS) | Arizona Public Service Company | Cholla |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Expected environmental cost |  |  |  |  |  | 8.0
Coal combustion waste | Arizona Public Service Company | Four Corners |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | 15.0
Coal combustion waste | Arizona Public Service Company | Navajo Plant |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | 1.0
Coal combustion waste | Arizona Public Service Company | Navajo Plant | Boron Inclusion on List of Groundwater Constituents |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Industry litigation, period to complete rulemaking proceeding |  |  | 3 years |  |  |
Coal combustion waste | Arizona Public Service Company | Cholla |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | $ 40.0
Payment Guarantee | Subsequent Event |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |
Number of parental guarantees | guarantee | 2 |  |  |  |  |

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