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Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) $ in Millions |  |  |  |  |  | 9 Months Ended
--- | --- | --- | --- | --- | --- | ---
Aug. 08, 2017 | Jun. 13, 2017 USD ($) | Apr. 28, 2017 | Jul. 06, 2016 guarantee | Jun. 24, 2016 | Sep. 30, 2017 USD ($)
Clean Power Plan |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Litigation abeyance period | 60 days |  | 60 days |  |  |
Periodic update period |  |  |  |  |  | 30 days
Coal Supply Agreement Arbitration | Four Corners |  |  |  |  |  |
Four Corners Coal Supply Agreement |  |  |  |  |  |
Damages sought |  | $ 30 |  |  |  |
Arizona Public Service Company | Coal Supply Agreement Arbitration | Four Corners |  |  |  |  |  |
Four Corners Coal Supply Agreement |  |  |  |  |  |
Damages sought |  | $ 17 |  |  |  |
Arizona Public Service Company | Letter of Credit Expiring in 2016 and 2017 |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |
Outstanding letters of credit |  |  |  |  |  | $ 5
Arizona Public Service Company | Letters of Credit Expiring in 2017 |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |
Surety bonds expiring, amount |  |  |  |  |  | $ 62
4C Acquisition, LLC | Four Corners Units 4 and 5 |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Percentage of share of cost of control |  |  |  |  |  | 7.00%
4C Acquisition, LLC | Four Corners |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Percentage of share of cost of control |  |  |  | 7.00% |  |
4C Acquisition, LLC | Coal Supply Agreement Arbitration | Four Corners |  |  |  |  |  |
Four Corners Coal Supply Agreement |  |  |  |  |  |
Reimbursement payments due to 4CA |  |  |  |  |  | $ 26
Reimbursement payments due to 4CA at end of current fiscal year |  |  |  |  |  | $ 10
NTEC | Four Corners |  |  |  |  |  |
Four Corners Coal Supply Agreement |  |  |  |  |  |
Option to purchase ownership interest (as a percent) |  |  |  | 7.00% |  |
NTEC | Coal Supply Agreement Arbitration | Four Corners |  |  |  |  |  |
Four Corners Coal Supply Agreement |  |  |  |  |  |
Option to purchase ownership interest (as a percent) |  |  |  | 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
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
Regional Haze Rules | Arizona Public Service Company | Navajo Plant |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Expected environmental cost |  |  |  |  |  | 200
Coal combustion waste | Arizona Public Service Company | Four Corners |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | 22
Coal combustion waste | Arizona Public Service Company | Navajo Plant |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | 1
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 |  |  |  |  | 2 years |
Minimum | Coal combustion waste | Arizona Public Service Company | Cholla |  |  |  |  |  |
Environmental Matters |  |  |  |  |  |
Site contingency increase in loss exposure not accrued, best estimate |  |  |  |  |  | $ 20
Payment Guarantee |  |  |  |  |  |
Financial Assurances |  |  |  |  |  |
Number of parental guarantees | guarantee |  |  |  | 4 |  |

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